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

1,2

Comments

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

Links

Table of n, a(n) for n=1..63.

Example

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.

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 *)

Crossrefs

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

Sequence in context: A002396 A302099 A029508 * A095714 A137864 A256154

Adjacent sequences: A256932 A256933 A256934 * A256936 A256937 A256938

Keyword

base,nonn

Author

Giovanni Teofilatto, Apr 13 2015

Status

approved