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A115709 Pentagonal numbers (A000326) whose digit reversal is a semiprime (A001358). 5
12, 22, 51, 176, 330, 532, 590, 715, 782, 925, 1162, 1247, 1335, 1426, 1717, 3151, 3290, 4187, 5551, 7107, 7315, 7957, 10542, 10795, 11051, 11837, 12376, 14950, 15251, 15555, 15862, 16172, 17120, 19097, 19780, 20126, 22265, 24130, 24512 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

EXAMPLE

532 is the 19th pentagonal number and 235=5*47 is semiprime.

MATHEMATICA

Select[PolygonalNumber[5, Range[200]], PrimeOmega[IntegerReverse[#]]==2&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jan 27 2019 *)

CROSSREFS

Cf. A000326, A001358, A115708.

Sequence in context: A129639 A153361 A200197 * A115703 A014633 A298323

Adjacent sequences:  A115706 A115707 A115708 * A115710 A115711 A115712

KEYWORD

nonn,base

AUTHOR

Giovanni Resta, Jan 31 2006

STATUS

approved

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Last modified December 2 02:12 EST 2021. Contains 349435 sequences. (Running on oeis4.)