A380303 Numbers m such that GCD of the solutions x to sigma(x) = sigma(m) are setwise coprime.

1, 6, 10, 11, 14, 15, 16, 17, 20, 21, 23, 24, 25, 26, 28, 30, 31, 33, 34, 35, 38, 39, 40, 41, 42, 44, 46, 47, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 62, 63, 65, 66, 69, 70, 71, 74, 76, 77, 78, 79, 83, 84, 85, 86, 87, 88, 89, 90, 92, 93, 94, 95, 96, 97, 99, 102, 103, 105, 107, 108, 110, 111, 112, 113, 114, 115, 117, 118, 119, 120, 123, 124, 125, 126, 127, 130, 131, 132, 135, 136, 138, 139, 140, 141, 142, 143, 145, 147, 150

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).

Formula

Union of {1} and the set difference of A206036 and A241481.

Prog

(PARI) isok(k) = if(k == 1, 1, my(v = invsigma(sigma(k))); #v > 1 && gcd(v) == 1); \\ Amiram Eldar, May 28 2025, using Max Alekseyev's invphi.gp (see links).

Crossrefs

Cf. A206036, A211656, A241480, A241481, A241625, A380304.

Sequence in context: A377421 A107014 A206036 * A349761 A132628 A288928

Adjacent sequences: A380300 A380301 A380302 * A380304 A380305 A380306

Keyword

nonn

Author

Max Alekseyev, Jan 19 2025

Status

approved