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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.
0
3, 13, 20, 42, 44, 45, 56, 60, 86, 87, 112, 119, 121
OFFSET
1,1
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