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
17 (number) the only prime number which is the sum of four consecutive primes (2,3,5,7). Any other four consecutive primes summed would always produce an even number, thereby divisible by 2 and so not prime. In Catalan, 17 is the first compound number ("disset"). The numbers 11 ("onze") through 16 ("setze") have their own names. In French, 17 is the first compound number ("dix-sept"). The numbers 11 ("onze") through 16 ("seize") have their own names. In Italian, 17 is also the first compound number ("diciassette"), whereas sixteen is "sedici". Seventeen is: 17 (number) 17 (seventeen) is the natural number following 16 and