A050691 Composite numbers whose decimal expansion starts with their largest prime divisor.

36, 50, 70, 110, 130, 170, 190, 230, 256, 290, 310, 324, 370, 384, 410, 430, 470, 500, 530, 540, 590, 610, 670, 700, 710, 730, 735, 756, 784, 790, 830, 890, 970, 1010, 1030, 1070, 1090, 1100, 1130, 1155, 1188, 1270, 1300, 1310, 1352, 1365, 1370, 1390, 1490

Offset

1,1

Links

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

Example

1188 = {11}88 = 2*2*3*3*3*{11}.

Mathematica

d[n_]:=IntegerDigits[n]; aQ[n_]:=!PrimeQ[n]&&Take[d[n], Length[y=d[Max@@First/@FactorInteger[n]]]]==y; Select[Range[2, 1500], aQ[#]&] (* Jayanta Basu, May 30 2013 *)
lpfQ[n_]:=Module[{c=IntegerDigits[FactorInteger[n][[-1, 1]]]}, CompositeQ[ n] && Take[IntegerDigits[n], Length[c]]==c]; Select[Range[1500], lpfQ] (* Harvey P. Dale, Dec 20 2014 *)

Crossrefs

Cf. A050692, A050693.

Sequence in context: A261292 A335249 A332287 * A211720 A261285 A261257

Adjacent sequences: A050688 A050689 A050690 * A050692 A050693 A050694

Keyword

nonn,base

Author

Patrick De Geest, Aug 15 1999

Status

approved