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A256935 Concatenation of odd prime factors of numbers whose digits are all odd. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified May 24 23:45 EDT 2020. Contains 334581 sequences. (Running on oeis4.)