A307624 Least number whose digits can be used to form exactly n distinct composite numbers (not necessarily using all digits).
1, 4, 12, 18, 46, 103, 122, 104, 102, 108, 124, 128, 126, 148, 246, 468, 1002, 1008, 1137, 1077, 1014, 1055, 1044, 1022, 1124, 1126, 1079, 1145, 1037, 1224, 1266, 1448, 1379, 1039, 1367, 1036, 1057, 1034, 1027, 1047, 1024, 1023, 1025, 1029, 1026, 1068, 1247, 1235, 3579, 1234, 1257, 1289, 1239, 1236, 1278, 1245
Offset: 0
Examples
The digits of 103 can be used to form the numbers 1, 3, 10, 13, 30, 31, 103, 130, 301, and 310. Of these, exactly 5 are composite (10, 30, 130, 301 = 7*43, and 310). Since 103 is the smallest such number, a(5) = 103.
Crossrefs
Programs
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Mathematica
f[n_] := Length[Union[ Select[FromDigits /@ Flatten[Permutations /@ Subsets[IntegerDigits[n]], 1], CompositeQ]]]; t = Table[0, {100}]; Do[ a = f[n]; If[a < 100 && t[[a + 1]] == 0, t[[a + 1]] = n], {n, 100000}]; t
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