A388975 a(n) = A033885(A003961(n)), where A033885(n) = 3*n-sigma(n), and A003961 is fully multiplicative with a(p) = nextprime(p).

2, 5, 9, 14, 13, 21, 21, 41, 44, 31, 25, 57, 33, 51, 57, 122, 37, 101, 45, 85, 93, 61, 57, 165, 90, 81, 219, 141, 61, 123, 73, 365, 111, 91, 135, 272, 81, 111, 147, 247, 85, 207, 93, 169, 277, 141, 105, 489, 230, 213, 165, 225, 117, 501, 161, 411, 201, 151, 121, 321, 133, 181, 453, 1094, 213, 249, 141, 253, 255

Offset

1,1

Comments

There are eventually negative terms. For example, at y = 13385572200 = A064989(x), where x = A119240(3) = 1018976683725 (the first odd term of A023197), with a(y) = -20872956825.

Links

Antti Karttunen, Table of n, a(n) for n = 1..16384

Index entries for sequences related to prime indices in the factorization of n.

Index entries for sequences related to sigma(n).

Formula

a(n) = A249734(n) - A003973(n) = A003961(2*n) - A000203(A003961(n)).

a(n) = A388977(n) / n.

Prog

(PARI)
A003961(n) = { my(f = factor(n)); for (i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); factorback(f); };
A033885(n) = (3*n-sigma(n));
A388975(n) = A033885(A003961(n));

Crossrefs

Cf. A003961, A003973, A023197, A033885, A064989, A119240, A249734, A388976, A388977.

Sequence in context: A364248 A284916 A070986 * A074793 A161767 A235333

Adjacent sequences: A388972 A388973 A388974 * A388976 A388977 A388978

Keyword

sign

Author

Antti Karttunen, Sep 22 2025

Status

approved