Sixty-one is prime and reduces to seven. Its principal traditional weight is again gematria: the Hebrew word ani, meaning I, is spelled aleph, nun, yod, one, fifty and ten, totalling sixty-one, so the number is associated with the first-person self and figures in Kabbalistic reflection on selfhood and its relation to ain, nothingness, whose letters differ. Beyond this the number has little developed lore; it is a prime that the older symbolic systems, apart from the gemat arithmeticians, did not take up.
In chemistry, sixty-one is the atomic number of promethium, named after Prometheus, the Titan who stole fire from the gods, a name chosen because the element was made in a nuclear reactor and was meant to evoke both the promise and the danger of the new nuclear age; the modern name was settled in 1950. Promethium is one of only two elements below atomic number eighty-three with no stable isotope at all, the other being technetium. Chemical proof of its existence came in 1945, though the finding was not announced until 1947, when Jacob Marinsky, Lawrence Glendenin and Charles Coryell isolated it from uranium fission products at the Clinton Laboratories in Oak Ridge, Tennessee.
Sixty-one is prime, with no factors beyond one and itself. It is a twin prime, paired with 59, a prime just two away. Because it leaves a remainder of one when divided by four, it is a Pythagorean prime, expressible as a sum of two squares: 5 squared plus 6 squared.