A119603 -id:A119603 - cp's OEIS frontend

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

Giovanni Teofilatto, Apr 14 2015

Numbers in the sequence m cannot have even digits and 1: {3, 5, 7, 9, 33, 35, 37, 39, 53, ..., 99, 333, 335, ...}.

Subset of A256935.

			a(5) = 33 because m(5) = 9, whose odd prime factors are 3 * 3, thus 33 is the concatenation of the factors.

Cf. A119603, A256935.

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 *)

A256935 Concatenation of odd prime factors of numbers whose digits are all odd.

Original entry on oeis.org

0, 3, 5, 7, 33, 11, 13, 35, 17, 19, 31, 311, 57, 37, 313, 317, 53, 511, 319, 59, 71, 73, 355, 711, 79, 713, 331, 519, 97, 3311, 337, 113, 523, 3313, 717, 131, 719, 3335, 137, 139, 151, 3317, 531, 157, 353, 3319, 173, 557, 359, 179, 191, 193, 3513, 197, 199, 311, 313, 3357, 317, 1129, 331, 3337, 567

Offset: 1

Giovanni Teofilatto, Apr 13 2015

In decimal digits of a(n) there is at least one prime.

			a(5) = 33 because the fifth odd number is 9, and the odd prime factors of 9 are 3 * 3, thus 33 is the result of the concatenation of these factors.

Cf. A119603, A256154 (Concatenation of odd prime factors of m such that the decimal digits of m only have odd prime factors).

f[n_] := Block[{of = Select[Table[#1, {#2}] & @@@ FactorInteger@ n // Flatten, PrimeQ@ # && # > 2 &]}, IntegerDigits@ of // Flatten // FromDigits]; f /@ Select[Range@ 360, OddQ[Times @@ IntegerDigits[#]] &] (* Michael De Vlieger, Apr 13 2015 *)

cp's OEIS Frontend

A256154 Concatenation of odd prime factors of m such that the decimal digits of m only have odd prime factors.

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