A069926 Number of k, 1<=k<=n, such that k divides sigma(k).

1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3

Offset

1,6

Comments

a(n) is the number of multiply-perfect numbers (A007691) <= n. - Robert Israel, Aug 29 2018

Links

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

Formula

a(n) = Card(k: 1<=k<=n : sigma(k) == 0 (mod k) ).

Prog

(PARI) for(n=1, 150, print1(sum(i=1, n, if(sigma(i)%(i), 0, 1)), ", "))

Crossrefs

Cf. A007691.

Sequence in context: A108248 A087104 A343743 * A077429 A204553 A214455

Adjacent sequences: A069923 A069924 A069925 * A069927 A069928 A069929

Keyword

easy,nonn

Author

Benoit Cloitre, May 05 2002

Status

approved