180 (number) two square numbers: 12 + 6. It can be expressed as either the sum of six consecutive prime numbers: 19 + 23 + 29 + 31 + 37 + 41, or the sum of eight consecutive prime numbers: 11 + 13 + 17 + 19 + 23 + 29 + 31 + 37. 180 is an Ulam number, which can be expressed as a sum of earlier terms in the Ulam sequence only as 177 + 3. 180 is a 61-gonal number. Half a circle has 180 degrees. Summing Euler's totient function φ("x") over the first + 24 integers gives
Prime number arts and literature. They have also been used in evolutionary biology to explain the life cycles of cicadas. Fermat primes are primes of the form with formula_64 a natural number. They are named after Pierre de Fermat, who conjectured that all such numbers are prime. The first five of these numbers – 3, 5, 17, 257, and 65,537 – are prime, but formula_236 is composite and so are all other Fermat numbers that have been verified as of 2017. A regular formula_1-gon is constructible using straightedge and compass if and only if the odd prime factors of formula_1 (if any)