A331019 a(n) is the least k such that the denominator(sigma(sigma(k*n))/(k*n)) equals n.

1, 15, 1, 8, 1, 144, 1, 16, 1, 1, 1, 8, 1, 255, 3, 16, 1, 12, 1, 2, 7, 1, 1, 288, 1, 18, 21, 8, 1, 84, 1, 13, 1, 11, 1, 4096, 1, 4, 3, 270, 1, 2448, 1, 2, 3, 1, 1, 16, 1, 420, 3, 1, 1, 124, 3, 16, 3, 128, 1, 616, 1, 85, 3, 16, 1, 1, 1, 8, 3, 1, 1, 32, 1, 64

Offset

1,2

Comments

a(n) is the least k such that the A318060(k*n) equals n.

Links

Ray Chandler, Table of n, a(n) for n = 1..10000

Formula

a(n) = A331033(n)/n.

Prog

(PARI) a(n) = my(k=n); while (denominator(sigma(sigma(k))/k) != n, k+=n); k/n;

Crossrefs

Cf. A000203 (sigma), A051027 (sigma(sigma)), A318060.

Cf. A019278, A330598, A331033.

Sequence in context: A040234 A040235 A040236 * A185903 A040237 A317835

Adjacent sequences: A331016 A331017 A331018 * A331020 A331021 A331022

Keyword

nonn

Author

Ray Chandler, Jan 09 2020

Status

approved