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A049328 Numbers whose prime factors (taken with multiplicity) sum to 20. 0
51, 91, 130, 154, 156, 220, 264, 297, 392, 441, 525, 560, 625, 630, 672, 750, 756, 800, 900, 960, 1024, 1080, 1152, 1215, 1296, 1458 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

Table of n, a(n) for n=1..26.

EXAMPLE

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

MATHEMATICA

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

CROSSREFS

Numbers k such that A001414(k) = 20.

Sequence in context: A039474 A253020 A020180 * A075894 A229274 A044140

Adjacent sequences:  A049325 A049326 A049327 * A049329 A049330 A049331

KEYWORD

fini,full,nonn

AUTHOR

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

EXTENSIONS

Corrected by Frank Ellermann, Jun 07 2001

Further corrected by N. J. A. Sloane, Jan 16 2019 at the suggestion of Harvey P. Dale.

STATUS

approved

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Last modified October 26 11:59 EDT 2021. Contains 348267 sequences. (Running on oeis4.)