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

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

Author

Giovanni Teofilatto, Apr 13 2015

Keywords

• base
• nonn

Comments

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

Examples

			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.
		

Crossrefs

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

Programs

Mathematica

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 *)