A115559 a(n) is here if it is not a prime number and it is an integer square root of an entry taken from A115557.

1, 316, 333, 549, 844, 963, 981, 1052, 1233, 1251, 1304, 1341, 1359, 1474, 1629, 1688, 1737, 1738, 1996, 2061, 2144, 2216, 2421, 2528, 2547, 2763, 2979, 3033, 3082, 3123, 3141, 3148, 3231, 3244, 3283, 3303, 3411, 3573, 3634, 3871, 3879, 3897, 3988, 4113

Offset

1,2

Links

Giovanni Resta, Table of n, a(n) for n = 1..10000

Formula

The commutator [sigma, tau] is zero and a(n) is the square root of solutions. Moreover this square root is a nonprime number.

Prog

(PARI) isok(n)= !isprime(n) && (sigma(numdiv(n^2)) == numdiv(sigma(n^2))); \\ Michel Marcus, Dec 20 2013

Crossrefs

Cf. A000005, A000203, A076360, A076361, A062068, A062069, A115557, A115559, A115560.

Sequence in context: A048905 A200314 A349419 * A033861 A179155 A237561

Adjacent sequences: A115556 A115557 A115558 * A115560 A115561 A115562

Keyword

nonn

Author

Labos Elemer, Jan 25 2006

Status

approved