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 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, 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 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified June 20 10:31 EDT 2024. Contains 373516 sequences. (Running on oeis4.)