A135591 a(n) is number of earlier terms equal to number of proper divisors of n.

1, 1, 2, 1, 3, 1, 4, 1, 1, 1, 7, 0, 7, 1, 1, 1, 10, 0, 10, 0, 1, 1, 12, 2, 2, 1, 1, 0, 14, 2, 14, 0, 1, 1, 1, 0, 17, 1, 1, 2, 19, 2, 19, 0, 0, 1, 20, 0, 6, 0, 1, 0, 21, 2, 1, 2, 1, 1, 24, 0, 24, 1, 0, 1, 1, 2, 27, 0, 1, 2, 28, 0, 28, 1, 0, 0, 1, 2, 30, 0, 1, 1, 32, 0, 1, 1, 1, 2, 35, 0, 1, 0, 1, 1, 1, 0, 39

Offset

1,3

Comments

Similar to A125087, but instead of exponents, we use number of proper divisors.

Links

Katarzyna Matylla, Table of n, a(n) for n = 1..1000

Example

a(12)=0 because 12 has 5 proper divisors (1, 2, 3, 4 and 6) and there is no 5 in a(1), a(2), ..., a(11).

Prog

(Maxima) max:1000; f:makelist(0, i, 1, max); apr:makelist(0, i, 0, max); f[1]:1; apr[2]:1; for n:2 through max do block(f[n]:apr[divsum(n, 0)], apr[f[n]+1]:apr[f[n]+1]+1);

Crossrefs

Cf. A125087.

Sequence in context: A325252 A355531 A234809 * A114897 A360614 A210954

Adjacent sequences: A135588 A135589 A135590 * A135592 A135593 A135594

Keyword

nonn

Author

Katarzyna Matylla, Feb 25 2008

Status

approved