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 A126433 Class+ number of prime(n) according to the Erdős-Selfridge classification of primes. 8
 1, 1, 1, 1, 1, 2, 1, 2, 1, 2, 1, 3, 2, 2, 1, 1, 2, 2, 2, 1, 4, 2, 2, 2, 2, 2, 3, 1, 2, 3, 1, 2, 2, 2, 2, 3, 3, 3, 2, 3, 2, 3, 1, 3, 2, 2, 2, 2, 3, 2, 3, 2, 2, 2, 3, 2, 2, 2, 3, 2, 2, 2, 2, 3, 4, 2, 3, 3, 3, 2, 3, 2, 2, 2, 3, 1, 3, 3, 3, 3, 2, 3, 1, 2, 2, 4, 2, 3, 2, 3, 3, 2, 3, 3, 2, 2, 2, 3, 3, 3, 3, 2, 2, 3, 3 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,6 COMMENTS a(n)=1 if A000040(n) is in A005105. a(n)=2 if A000040(n) is in A005106, a(n)=3 if in A005107 etc. The locations of records are implicit in A005113. LINKS M. F. Hasler, Table of n, a(n) for n = 1..1000 Index entries for sequences related to the Erdos-Selfridge classification MAPLE A126433 := proc(n) option remember; local p, pf, e, a; if isprime(n) then pf := ifactors(n+1)[2]; a := 1; for e from 1 to nops(pf) do p := op(1, op(e, pf)); if p > 3 then a := max(a, procname(p)+1); end if; end do; a ; else -1; end if; end proc: seq(A126433(ithprime(n)), n=1..100) ; A126433 := n -> if n>0 then A126433(-ithprime(n)) else numtheory[factorset](1-n); if % subset{2, 3} then 1 else 1+max(seq(A126433(-i), i=%)) fi fi; map(%, [\$1..999]); # M. F. Hasler, Apr 02 2007 MATHEMATICA classPlus[p_] := classPlus[p] = If[f = FactorInteger[p + 1][[All, 1]]; q = Last[f]; q == 2 || q == 3, 1, Max[classPlus /@ f] + 1]; classPlus /@ Prime /@ Range[105] (* Jean-François Alcover, Jun 24 2013 *) PROG (PARI) A126433(n) = { if( n>0, n=-prime(n)); n=factor(1-n)[, 1]; if( n[ #n]>3, vecsort( vector( #n, i, A126433(-n[i]) ))[ #n]+1, 1) }; vector(999, i, A126433(i)) CROSSREFS Cf. A101253. Sequence in context: A023124 A023120 A167970 * A237271 A336041 A176725 Adjacent sequences: A126430 A126431 A126432 * A126434 A126435 A126436 KEYWORD nonn AUTHOR R. J. Mathar, Mar 23 2007 STATUS approved

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Last modified July 15 16:08 EDT 2024. Contains 374333 sequences. (Running on oeis4.)