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

Author

Gary W. Adamson, Jun 14 2007

Keywords

• nonn

Comments

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

Examples

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

Crossrefs

Row sums of triangle A131088.

Cf. A062011, A051731, A131090, A228483.

Programs

Magma

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

Mathematica

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

PARI

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

Formula

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

Inverse Moebius transform of A228483.

Extensions

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