21159

Appears in sequences

• Starting numbers for which the RATS sequence has eventual period 3.at n=2A114613
• a(n) = 40*n^2 - 1.at n=22A158598
• Number of 1X5 integer matrices with each row summing to zero, row elements in nondecreasing order, rows in lexicographically nondecreasing order, and the sum of squares of the elements <= 2*n^2 (number of collections of 1 zero-sum 5-vectors with total modulus squared not more than 2*n^2, ignoring vector and component permutations).at n=22A192692
• Numbers of the form HMMSS with primes H < 24 and MM, SS < 60, for which the number of seconds after midnight, 3600*H+60*MM+SS, is also prime.at n=27A295011
• Sociable totient numbers of order 3: numbers k such that s(s(s(k))) = k, but s(k) != k, where s(k) = A092693(k) is the sum of iterated phi function.at n=1A343243