A105852 a(n) = sigma(n) mod 9.

1, 3, 4, 7, 6, 3, 8, 6, 4, 0, 3, 1, 5, 6, 6, 4, 0, 3, 2, 6, 5, 0, 6, 6, 4, 6, 4, 2, 3, 0, 5, 0, 3, 0, 3, 1, 2, 6, 2, 0, 6, 6, 8, 3, 6, 0, 3, 7, 3, 3, 0, 8, 0, 3, 0, 3, 8, 0, 6, 6, 8, 6, 5, 1, 3, 0, 5, 0, 6, 0, 0, 6, 2, 6, 7, 5, 6, 6, 8, 6, 4, 0, 3, 8, 0, 6, 3, 0, 0, 0, 4, 6, 2, 0, 3, 0, 8, 0, 3, 1, 3, 0, 5, 3, 3

Offset: 1

Author

Shyam Sunder Gupta, May 05 2005

Keywords

• easy
• nonn

Comments

If gcd(m,n) = 1 then a(m*n) = (a(m) * a(n)) mod 9. - Robert Israel, Sep 14 2014

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000203, A010878, A190998 (digital root of sigma(n)).

Programs

Maple

seq(numtheory:-sigma(n) mod 9, n=1..1000); # Robert Israel, Sep 14 2014

Mathematica

Mod[DivisorSigma[1, Range[100]], 9] (* Wesley Ivan Hurt, Apr 25 2023 *)

PARI

a(n)=sigma(n)%9

Formula

a(n) = A010878(A000203(n)). - Michel Marcus, Sep 14 2014

Extensions

Name corrected and keyword base removed by Michel Marcus, Sep 14 2014