A050693 Composites c whose decimal expansion ends with its largest prime factor.

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

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: A366926 A102802 A050692 * A200046 A349750 A171133

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