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A050691
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Composite numbers whose decimal expansion starts with their largest prime divisor.
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3
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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
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OFFSET
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1,1
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LINKS
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EXAMPLE
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1188 = {11}88 = 2*2*3*3*3*{11}.
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MATHEMATICA
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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 *)
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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