A062238 Composite numbers which contain their largest proper divisor as a substring.

15, 25, 125, 1537, 3977, 11371, 38117, 110317, 117197, 123679, 143323, 146137, 179297, 197513, 316619, 390913, 397139, 399797, 485357, 779917, 797191, 990919, 1110691, 1178951, 1483117, 1723717, 1813733, 2165299, 2273099, 2369777, 2947969, 3035171, 3099013, 3183113

Offset: 1

Author

Erich Friedman, Jun 30 2001

Keywords

• base
• nonn

Examples

			3{97}7 = 97*41.
		

Links

• Michel Marcus, Table of n, a(n) for n = 1..272

Crossrefs

Cf. A002808 (composite numbers), A032742.

Programs

Mathematica

Do[ If[ !PrimeQ[ n ] && StringPosition[ ToString[ n ], ToString[ Divisors[ n ] [ [ -2 ] ] ] ] != {}, Print[ n ] ], {n, 2, 10^7} ]
Select[Range[319*10^4],CompositeQ[#]&&SequenceCount[IntegerDigits[ #],IntegerDigits[ Divisors[#][[-2]]]]>0&] (* Harvey P. Dale, Dec 26 2022 *)

PARI

gpd(n) = if(n==1, 1, n/factor(n)[1, 1]); \\ A032742
issub(vv, v) = {for (i=1, #v - #vv + 1, if (vector(#vv, k, v[k+i-1]) == vv, return(1)););}
isok(n) = if ((n>1) && !isprime(n), issub(digits(gpd(n)), digits(n))); \\ Michel Marcus, Dec 31 2020

Extensions

More terms from Robert G. Wilson v, Aug 08 2001

More terms from Michel Marcus, Dec 31 2020

Clarified definition at the suggestion of Harvey P. Dale. - N. J. A. Sloane, Dec 26 2022