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A087173
Smallest prime factor of n-th partition number.
3
1, 2, 3, 5, 7, 11, 3, 2, 2, 2, 2, 7, 101, 3, 2, 3, 3, 5, 2, 3, 2, 2, 5, 3, 2, 2, 2, 2, 5, 2, 2, 3, 3, 2, 3, 17977, 7, 5, 3, 2, 3, 2, 3, 5, 2, 2, 2, 3, 5, 2, 3, 3, 3, 5, 2, 11, 2, 2, 2, 17, 3, 2, 3, 2, 2, 2, 1181, 3, 5, 2, 3, 11, 23, 2, 2, 7, 10619863, 2, 2, 2, 11, 5, 7, 2, 11, 2, 11, 3, 5, 2473
OFFSET
1,2
LINKS
Eric Weisstein's World of Mathematics, Least Prime Factor
Eric Weisstein's World of Mathematics, Partition Function
Eric Weisstein's World of Mathematics, Partition Function P Congruences
FORMULA
a(n) = A020639(A000041(n)).
EXAMPLE
A000041(100) = 190569292 = 2*2*43*59*89*211, therefore a(100)=2.
MATHEMATICA
FactorInteger[#][[1, 1]]&/@PartitionsP[Range[90]] (* Harvey P. Dale, May 20 2023 *)
PROG
(PARI) spf(n) = if (n==1, 1, vecmin(factor(n)[, 1]));
a(n) = spf(numbpart(n)); \\ Michel Marcus, Feb 24 2023
CROSSREFS
Cf. A071963.
Sequence in context: A194261 A194262 A039710 * A179335 A330994 A097858
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Aug 23 2003
STATUS
approved