No 73 Emerald Hill, Singapore … a prime number that is also a star number (Photograph: Patrick Comerford, 2024)
Patrick Comerford
We RE on our way to the Holocaust Remembrance Day commemorations in Milton Keynes, which may not be the most joyful way to mark or celebrate my birthday this afternoon. Perhaps we shall go for a meal out later in the day, and have a drink in Stony Stratford on the way home to mark the evening.
Shakespeare talks in Sonnet 73 of
… … the twilight of such day
As after sunset fadeth in the west
But I have a lot to be thankful for on this birthday as I look back over the last 73 years.
In those 73 years, I have lived through the reign, rule or time in office of three British monarchs, seven Popes, seven (soon to be eight) Archbishops of Canterbury, eight Irish Presidents, eight Church of Ireland Archbishops of Armagh, 14 (or 15) US Presidents (depending on how you count Trum), 16 Greek heads of state, 17 Taoisigh, 18 British Prime Ministers … it almost sounds like singing out the 12 days of Christmas.
Despite Shakespeare’s words, I still feel as though I am in the prime of my life, as befits reaching yet another prime number, rather than in ‘the twilight of such day’ or even ‘after sunset fadeth in the west’.
The number 73 is a natural number, a prime number, and is what is known in mathematics as a star number, a twin prime, a lucky prime and a sexy prime. It also the number of books in the Catholic Bible, and another way of saying ‘best regards’ when signing off some conversations.
73 as a star number (up to blue dots) … 37, its dual permutable prime, is the preceding consecutive star number (up to green dots)
In mathematics, 73 is the 21st prime number, and an emirp – a prime number that results in a different prime when its decimal digits are reversed – with 37, the 12th prime number. It is also the eighth twin prime, with 71 – a twin prime is a prime number that is either 2 less or 2 more than another prime number, such as either member of the twin prime pair 17 and 19, 41 and 43, or 71 and 73.
The number 73 is the fourth star number. In mathematics, a star number is a centred figurate number, a centred hexagram (six-pointed star), such as the Star of David, or the board Chinese checkers is played on. The numbers 73 and 37 are also consecutive star numbers or equivalently consecutive centred dodecagonal (12-gonal) numbers, respectively the fourth and the third.
The numbers 73 and 37 are successive lucky primes and sexy primes, both twice over. In number theory, a lucky number is a natural number in a set that is generated by a certain ‘sieve’, similar to the sieve of Eratosthenes that generates the primes, but eliminating numbers based on their position in the remaining set, instead of their value. And, in number theory, sexy primes are prime numbers that differ from each other by 6. For example, the numbers 5 and 11 are a pair of sexy primes, because both are prime and 11 – 5 = 6. In the same way, 73 - 67 = 6, and 79 - 73 = 6.
73 at a front door in Stony Stratford (Photograph: Patrick Comerford, 2025)
Amateur radio operators and other morse code users commonly use the number 73 as a ‘92 Code’ abbreviation for ‘best regards’, typically when ending a QSO or a conversation with another operator.
No 73 was a 1980s children's television programme on the ITV network that ran from 1982 to 1988.
In 1982, the TV Times summed up the show: ‘From the outside No. 73 looks like a tumbledown house, but once inside it’s a different world. The house, in the south of England, is rented by an eccentric old lady called Ethel, who is like a fairy godmother to the children in the area.
‘Each week she opens her door and is visited by superstars and famous personalities who provide a madcap spectacle of music, competitions and fun. Ethel is assisted in looking after her guests by her nephew Harry and her boyfriend Percy.’
73, paired with 75, on a front door in York (Photograph: Patrick Comerford, 2025)
In Sonnet 73, William Shakespeare focuses on the theme of old age and uses autumn, twilight and a dying fire as extended metaphors for growing older.
The poet invokes a series of metaphors to characterise the nature of what he sees as his old age. Each of the three quatrains contains a metaphor: Autumn, the passing of a day, and the dying out of a fire. Each metaphor proposes a way the younger person may see the poet.
Sonnet 73, ‘That time of year thou mayst in me behold’, by William Shakespeare:
That time of year thou mayst in me behold
When yellow leaves, or none, or few, do hang
Upon those boughs which shake against the cold,
Bare ruin’d choirs, where late the sweet birds sang.
In me thou see’st the twilight of such day
As after sunset fadeth in the west,
Which by and by black night doth take away,
Death’s second self, that seals up all in rest.
In me thou see’st the glowing of such fire
That on the ashes of his youth doth lie,
As the death-bed whereon it must expire,
Consum’d with that which it was nourish’d by.
This thou perceiv’st, which makes thy love more strong,
To love that well which thou must leave ere long.
‘As after sunset fadeth in the west’ … sunset on the Sarawak River in Kuching (Photograph: Patrick Comerford, 2024)
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