A256154 Concatenation of odd prime factors of m such that the decimal digits of m only have odd prime factors.
3, 5, 7, 33, 311, 57, 37, 313, 53, 511, 319, 59, 73, 355, 711, 79, 331, 519, 97, 3311, 3337, 567, 337, 3113, 353, 571, 3717, 359, 373, 3555, 1329, 379, 3131, 579, 397, 3719, 1341, 5107, 3179, 7711, 779, 3537, 557, 1343, 3191, 5523, 577, 3193, 593, 5717, 3199, 599, 733, 3577, 1167, 739, 3251, 5151
Offset: 1
Examples
a(5) = 33 because m(5) = 9, whose odd prime factors are 3 * 3, thus 33 is the concatenation of the factors.
Programs
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Mathematica
f[n_] := Block[{of = Select[Table[#1, {#2}] & @@@ FactorInteger@ n // Flatten, PrimeQ@ # && # > 2 &]}, IntegerDigits@ of // Flatten // FromDigits]; f /@ Select[Range@ 755, Plus @@ Pick[DigitCount@#, {1, 1, 0, 1, 0, 1, 0, 1, 0, 1}, 1] == 0 &] (* Michael De Vlieger, Apr 14 2015 *)
Comments