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A050693 Composites c whose decimal expansion ends with its largest prime factor. 3
15, 25, 32, 45, 75, 125, 135, 147, 225, 243, 375, 405, 512, 567, 625, 675, 1125, 1215, 1875, 2025, 3087, 3125, 3375, 3645, 5625, 6075, 8192, 9375, 10125, 10935, 11907, 12943, 13013, 13467, 14147, 14271, 14673, 15625, 15879, 15953, 16683, 16807 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The sequence is infinite because the numbers of the form 5^k, k >= 2, 3^(4*m + 1), m >= 1, 7^(4*s + 1), s >= 1, 3^(4*a) * 5^b, a, b >= 1, are terms. - Marius A. Burtea, Oct 18 2019

LINKS

David A. Corneth, Table of n, a(n) for n = 1..10000

EXAMPLE

16683 = 166{83} = 3*67*{83}.

MATHEMATICA

d[n_]:=IntegerDigits[n]; aQ[n_]:=!PrimeQ[n]&&Take[d[n], -Length[y=d[Max@@First/@FactorInteger[n]]]]==y; Select[Range[2, 16820], aQ[#]&] (* Jayanta Basu, May 31 2013 *)

PROG

(MAGMA) [k:k in [2..10000]| not IsPrime(k) and   k mod  10 ^(#Intseq(a)) eq a where a is Max(PrimeDivisors(k))]; // Marius A. Burtea, Oct 18 2019

(PARI) is(n) = {my(f = factor(n)); n % 10^(#digits(f[#f~, 1])) == f[#f~, 1] && !isprime(n)} \\ David A. Corneth, Oct 18 2019

CROSSREFS

Cf. A050691, A050692.

Sequence in context: A325571 A102802 A050692 * A200046 A171133 A152246

Adjacent sequences:  A050690 A050691 A050692 * A050694 A050695 A050696

KEYWORD

nonn,base

AUTHOR

Patrick De Geest, Aug 15 1999

EXTENSIONS

Name edited by Michel Marcus, Oct 18 2019

STATUS

approved

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Last modified September 23 08:23 EDT 2021. Contains 347610 sequences. (Running on oeis4.)