A228483 -id:A228483 - cp's OEIS frontend

A131089 a(n) = Sum_{d|n} (2 - mu(d)).

1, 4, 4, 6, 4, 8, 4, 8, 6, 8, 4, 12, 4, 8, 8, 10, 4, 12, 4, 12, 8, 8, 4, 16, 6, 8, 8, 12, 4, 16, 4, 12, 8, 8, 8, 18, 4, 8, 8, 16, 4, 16, 4, 12, 12, 8, 4, 20, 6, 12, 8, 12, 4, 16, 8, 16, 8, 8, 4, 24, 4, 8, 12, 14, 8, 16, 4, 12, 8, 16, 4, 24, 4, 8, 12, 12, 8, 16

Offset: 1

Gary W. Adamson, Jun 14 2007

nonn

Apart from the first term the same as A062011. - Andrew Howroyd, Aug 09 2018

			a(4) = 6 = (2 + 3 + 0 + 1), row 4 of A131088.

Row sums of triangle A131088.

Cf. A062011, A051731, A131090, A228483.

[1] cat [2*NumberOfDivisors(n) : n in [2..100] ]; // Vincenzo Librandi, Aug 10 2018

Join[{1}, Table[2 DivisorSigma[0, n], {n, 100}]] (* Vincenzo Librandi, Aug 10 2018 *)

a(n)={2*numdiv(n) - (n==1)} \\ Andrew Howroyd, Aug 09 2018

a(n) = 2*tau(n) = A062011(n) for n > 1. - Andrew Howroyd, Aug 09 2018

Inverse Moebius transform of A228483.

Name changed and terms a(10) and beyond from Andrew Howroyd, Aug 09 2018

A255369 a(n) = (sigma(n)-n-1)*(2-mu(n)), where sigma(n) is the sum of the divisors of n and mu(n) is the Möbius function.

Original entry on oeis.org

-1, 0, 0, 4, 0, 5, 0, 12, 6, 7, 0, 30, 0, 9, 8, 28, 0, 40, 0, 42, 10, 13, 0, 70, 10, 15, 24, 54, 0, 123, 0, 60, 14, 19, 12, 108, 0, 21, 16, 98, 0, 159, 0, 78, 64, 25, 0, 150, 14, 84, 20, 90, 0, 130, 16, 126, 22, 31, 0, 214, 0, 33, 80, 124, 18, 231, 0, 114

Offset: 1

Wesley Ivan Hurt, May 04 2015

sign

a(n) = 0 if and only if n is prime. If n is semiprime, then a(n) = sopfr(n).

Antti Karttunen, Table of n, a(n) for n = 1..65537
Antti Karttunen, Sequence plotted up to n=10000, showing the details better

Cf. A000203 (sigma), A008683 (Möbius function), A001414 (sopfr).

Cf. A048050 (Chowla's function), A228483 (2-mu(n)).

[(SumOfDivisors(n)-n-1)*(2-MoebiusMu(n)): n in [1..80]]; // Vincenzo Librandi, May 05 2015

with(numtheory): a:=n->(sigma(n)-n-1)*(2-mobius(n)): seq(a(n), n=1..100);

Table[(DivisorSigma[1, n] - n - 1) (2 - MoebiusMu[n]), {n, 100}]

a(n)=(sigma(n)-n-1)*(2-moebius(n)) \\ Dana Jacobsen, May 13 2015

use ntheory ":all"; say +(divisor_sum($)-$-1)*(2-moebius($)) for 1..80;  # _Dana Jacobsen, May 13 2015

a(n) = A048050(n) * A228483(n) for n > 1, a(1) = -1.

Formula corrected for case n=1 by Antti Karttunen, Feb 25 2018

cp's OEIS Frontend

A131089 a(n) = Sum_{d|n} (2 - mu(d)).

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