A215567 - OEIS

A215567

Numbers k with the property that k and the k-th number which is a product of k primes have the largest prime divisor and with the same multiplicity.

3, 13, 20, 42, 44, 45, 56, 60, 86, 87, 112, 119, 121

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OFFSET

1,1

LINKS

EXAMPLE

13 and the 13th 13-almost prime = 13*2^12 = 53248 have same largest prime factor = 13, with the same multiplicity, so 13 is a term.

MATHEMATICA

AlmostPrimePi[k_Integer, n_]:=...; AlmostPrime[k_, n_]:=...;

fQ[n_]:=FactorInteger[n][[-1, 1]]==FactorInteger[AlmostPrime[n, n]][[-1, 1]]; k=1; lst={};

While[k<150, If[fQ@k, AppendTo[lst, k]; Print@k]; k++]; lst (* Robert G. Wilson v, Aug 27 2012 *)

CROSSREFS

KEYWORD

nonn,less

AUTHOR

EXTENSIONS

a(9)-a(13) from Robert G. Wilson v, Aug 27 2012

Definition clarified by N. J. A. Sloane, Sep 04 2012

STATUS

approved