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A049328 Numbers whose prime factors (taken with multiplicity) sum to 20. 0

%I #14 Jan 17 2019 10:29:04

%S 51,91,130,154,156,220,264,297,392,441,525,560,625,630,672,750,756,

%T 800,900,960,1024,1080,1152,1215,1296,1458

%N Numbers whose prime factors (taken with multiplicity) sum to 20.

%C Numbers whose prime factorization k = 2^i_1 * 3^i_2 * 5^i_3 * .. * 17^i_7 * 19^i_8 satisfies 2*i_1 + 3*i_2 + ... + 17*i_7 + 19*i_8 = 20. - _N. J. A. Sloane_, Jan 16 2019

%e E.g. 51 = 3 * 17 and 3 + 17 = 20. 1024 = 2^10 and 10*2 = 20.

%t pfs20Q[n_]:=Total[#[[1]]#[[2]]&/@FactorInteger[n]]==20; Select[Range[ 10000],pfs20Q] (* _Harvey P. Dale_, Jan 17 2019 *)

%Y Numbers k such that A001414(k) = 20.

%K fini,full,nonn

%O 1,1

%A Rawlyn Watson (rawlyn(AT)chplayers.freeserve.co.uk)

%E Corrected by _Frank Ellermann_, Jun 07 2001

%E Further corrected by _N. J. A. Sloane_, Jan 16 2019 at the suggestion of _Harvey P. Dale_.

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Last modified July 13 04:46 EDT 2024. Contains 374267 sequences. (Running on oeis4.)