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

1,1

Links

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

Example

3{97}7 = 97*41.

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 *)

Prog

(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

Crossrefs

Cf. A002808 (composite numbers), A032742.

Sequence in context: A032587 A336689 A347375 * A146249 A248834 A249109

Adjacent sequences: A062235 A062236 A062237 * A062239 A062240 A062241

Keyword

base,nonn

Author

Erich Friedman, Jun 30 2001

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

Status

approved