A325977 - OEIS

A325977

a(n) = (1/2)*(A034448(n)+A048250(n)-2*n), where A034448 is the sum of unitary divisors and A048250 is the sum of squarefree divisors.

0, 1, 1, 0, 1, 6, 1, -2, -2, 8, 1, 4, 1, 10, 9, -6, 1, 3, 1, 4, 11, 14, 1, 0, -9, 16, -11, 4, 1, 42, 1, -14, 15, 20, 13, -5, 1, 22, 17, -4, 1, 54, 1, 4, -3, 26, 1, -8, -20, -2, 21, 4, 1, -6, 17, -8, 23, 32, 1, 36, 1, 34, -7, -30, 19, 78, 1, 4, 27, 74, 1, -21, 1, 40, -11, 4, 19, 90, 1, -20, -38, 44, 1, 44, 23, 46, 33, -16, 1, 36, 21, 4

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,6

COMMENTS

Question: Are n = 1, 4, 24, 240, 349440 (A325963) the only positions of zeros in this sequence?

LINKS

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

Antti Karttunen, Data supplement: n, a(n) computed for n = 1..65537

FORMULA

a(n) = (1/2)*(A034460(n) + A325313(n)).

a(n) = A325973(n) - n.

a(n) = A325978(n) - A033879(n).

Sum_{k=1..n} a(k) ~ c * n^2, where c = (zeta(2)/zeta(3) - 1)/4 = 0.0921081944... . - Amiram Eldar, Feb 22 2024

a(n) = (1/2)*(A034448(n)+A048250(n)-2*n). - Antti Karttunen, Sep 29 2025

MATHEMATICA

Array[(1/2) If[# == 1, 2, Times @@ (1 + Power @@@ #2) - 2 #1 + Times @@ (1 + #2[[;; , 1]]) & @@ {#, FactorInteger[#]}] &, 90] (* Michael De Vlieger, Jun 06 2019, after Giovanni Resta at A034448 and Amiram Eldar at A048250. *)

PROG

(PARI) A325977(n) = ((A034460(n)+A325313(n))/2);

(PARI)

A034448(n) = { my(f=factorint(n)); prod(k=1, #f~, 1+(f[k, 1]^f[k, 2])); };

A048250(n) = factorback(apply(p -> p+1, factor(n)[, 1]));

A325977(n) = ((A034448(n)+A048250(n)-2*n))/2;

(PARI) A325977(n) = (((1/2)*sumdiv(n, d, d*(issquarefree(d) + (1==gcd(d, n/d)))))-n); \\ Antti Karttunen, Sep 30 2025

CROSSREFS