A067565 Inverse of R. L. Graham's sequence (A006255), or zero if and only if n is a prime.

1, 0, 0, 4, 0, 2, 0, 3, 9, 5, 0, 6, 0, 7, 8, 16, 0, 10, 0, 12, 14, 11, 0, 15, 25, 13, 18, 21, 0, 20, 0, 24, 22, 17, 27, 36, 0, 19, 26, 28, 0, 30, 0, 33, 32, 23, 0, 35, 49, 40, 34, 39, 0, 48, 44, 42, 38, 29, 0, 45, 0, 31, 50, 64, 52, 55, 0, 51, 46, 54

Offset: 1

Author

Robert G. Wilson v, Jan 30 2002

Keywords

• nonn

Comments

a(n) = n if and only if n is a perfect square.

Also, the greatest m such that there exists a sequence m = a_1 < a_2 < ... < a_t = n such that a_1 * a_2 * ... * a_t is square. - Peter Kagey, Dec 27 2016

Links

• Peter Kagey, Table of n, a(n) for n = 1..5000

Crossrefs

Cf. A006255.