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

1,2

Comments

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

Links

Table of n, a(n) for n=1..78.

Formula

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

Inverse Moebius transform of A228483.

Example

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

Mathematica

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

Prog

(PARI) a(n)={2*numdiv(n) - (n==1)} \\ Andrew Howroyd, Aug 09 2018
(Magma) [1] cat [2*NumberOfDivisors(n) : n in [2..100] ]; // Vincenzo Librandi, Aug 10 2018

Crossrefs

Row sums of triangle A131088.

Cf. A062011, A051731, A131090, A228483.

Sequence in context: A077553 A010659 A255014 * A256486 A204068 A066560

Adjacent sequences: A131086 A131087 A131088 * A131090 A131091 A131092

Keyword

nonn

Author

Gary W. Adamson, Jun 14 2007

Extensions

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

Status

approved