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
400 (number) = 2 × 101, Mertens function returns 0, nontotient, noncototient. 405 = 3 × 5, Mertens function returns 0, Harshad number; 406 = 2 × 7 × 29, sphenic number, triangular number, centered nonagonal number, nontotient 407 = 11 × 37, 408 = 2 × 3 × 17 409 is a prime number, Chen prime, centered triangular number. 410 = 2 × 5 × 41, sphenic number, sum of six consecutive primes (59 + 61 + 67 + 71 + 73 + 79), nontotient, Harshad number 411 = 3 × 137, self number, 412 = 2 × 103, nontotient, noncototient,