On December 7, 1853, Gauss wrote a letter to Alexander von Humboldt with some kind of very particular greetings. He started noting that the celebration of birthdays had some clearly arbitrary character. (K. Bruhns (ed.), Briefe zwischen A. v. Humboldt und Gauss. Engelmann: Leipzig, 1877, 67–68.)
The artist of measure, in whose eyes vagueness and arbitrariness—in contrast to sharpness and firmness—always have some repulsive character, finds some evil in the fact that the reason that we fix this day, and not some other day, for the celebration is arbitrary. It depends on the organization of our calendar, the distribution of leap years, and as far as anniversaries are concerned, on the decimal system, that is, in the last instance, in the fact that we have five fingers on each hand.
He then tries to justify his greetings for the next December 9 on a more firm basis:
I cannot stop celebrating, with deep emotion, the ninth of December a day whose poignant meaning is not bound to such arbitrariness. This is the day in which you, my esteemed friend, [ . . . ] will reach the same age in which Newton closed his earthly career of 30,766 days.
My quest for a similar “ergreifende Bedeutung” for April 13, 2019 was a failure— but not a total failure. I had to go back to arbitrariness: if my calculations are right, the distance between December 7, 1928, and April 13, 2019, both included, is exactly 33,000 days! Happy 33,000th birthday!