A157137 Odd composite numbers k such that k and prime(k) have the same number of prime digits.

15, 33, 39, 45, 75, 81, 85, 93, 115, 117, 123, 133, 141, 145, 169, 183, 185, 187, 195, 205, 207, 209, 213, 231, 243, 247, 259, 261, 273, 275, 287, 289, 295, 299, 301, 315, 321, 325, 333, 335, 339, 343, 363, 365, 385, 387, 391, 395, 427, 477, 505, 517, 527

Offset

1,1

Comments

Prime digits are 2, 3, 5 or 7.

Links

Table of n, a(n) for n=1..53.

Example

15 is a term: prime(15)=47, and 15 and 47 each have one prime digit.
33 is a term: prime(33)=137, and 33 and 137 each have two prime digits.
39 is a term: prime(39)=167, and 39 and 167 each have two prime digits.

Crossrefs

Cf. A000027, A000040, A155548.

Sequence in context: A089967 A064900 A277254 * A141230 A140608 A085371

Adjacent sequences: A157134 A157135 A157136 * A157138 A157139 A157140

Keyword

nonn,base

Author

Juri-Stepan Gerasimov, Feb 24 2009

Extensions

Corrected by R. J. Mathar, Feb 26 2009

Edited by Jon E. Schoenfield, Apr 18 2021

Status

approved