A121599 a(n) = number of earlier terms which are not divisible by the smallest prime dividing n, for n >= 2, with a(1) = 1.

1, 1, 2, 2, 4, 2, 6, 2, 7, 3, 10, 4, 12, 4, 11, 5, 16, 6, 18, 6, 14, 6, 22, 6, 22, 6, 17, 7, 28, 8, 30, 8, 22, 8, 31, 9, 36, 10, 26, 10, 40, 10, 42, 10, 31, 11, 46, 12, 43, 13, 36, 14, 52, 14, 46, 14, 41, 15, 58, 16, 60, 16, 45, 17, 53, 19, 66, 20, 49, 21, 70, 22, 72, 22, 53, 23, 65

Offset

1,3

Links

Table of n, a(n) for n=1..77.

Formula

a(p) = p - 1 for p prime. - Petros Hadjicostas, May 11 2020

Example

2 is the smallest prime dividing 12. Among the first 11 terms of the sequence there are 4 terms (1, 1, 7, 3) that are not divisible by 2. So a(12) = 4.

Mathematica

f[s_] := Append[s, Length@ Select[s, Mod[ #, FactorInteger[1 + Length@s][[1, 1]]] != 0 &]]; Nest[f, {1}, 76] (* Robert G. Wilson v *)

Prog

(PARI) {m=78; print1(a=1, ", "); v=[a]; for(n=2, m, p=factor(n)[1, 1]; a=0; for(j=1, n-1, if(v[j]%p>0, a++)); print1(a, ", "); v=concat(v, a))} \\ Klaus Brockhaus, Aug 15 2006

Crossrefs

Cf. A096216, A121600.

Sequence in context: A117004 A128982 A096216 * A360593 A080221 A137849

Adjacent sequences: A121596 A121597 A121598 * A121600 A121601 A121602

Keyword

nonn

Author

Leroy Quet, Aug 09 2006

Extensions

More terms from Klaus Brockhaus and Robert G. Wilson v, Aug 15 2006

Status

approved