A388977 a(n) = n * A033885(A003961(n)), where A033885(n) = 3*n-sigma(n), and A003961 is fully multiplicative with a(p) = nextprime(p).

2, 10, 27, 56, 65, 126, 147, 328, 396, 310, 275, 684, 429, 714, 855, 1952, 629, 1818, 855, 1700, 1953, 1342, 1311, 3960, 2250, 2106, 5913, 3948, 1769, 3690, 2263, 11680, 3663, 3094, 4725, 9792, 2997, 4218, 5733, 9880, 3485, 8694, 3999, 7436, 12465, 6486, 4935, 23472, 11270, 10650, 8415, 11700, 6201, 27054, 8855

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) = -279396470608520265000.

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) = n * A388975(n).

a(n) = 3*A191002(n) - A341528(n) = (n*A003961(2*n)) - A341528(n).

a(n) >= A388976(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));
A388977(n) = n*A033885(A003961(n));

Crossrefs

Cf. A000203, A003961, A023197, A033885, A064989, A119240, A191002, A249734, A341528, A388975, A388976.

Sequence in context: A099583 A328743 A133479 * A196324 A327841 A196648

Adjacent sequences: A388974 A388975 A388976 * A388978 A388979 A388980

Keyword

sign

Author

Antti Karttunen, Sep 22 2025

Status

approved