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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
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
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.)