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A157137
Odd composite numbers k such that k and prime(k) have the same number of prime digits.
0
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.
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
KEYWORD
nonn,base
AUTHOR
EXTENSIONS
Corrected by R. J. Mathar, Feb 26 2009
Edited by Jon E. Schoenfield, Apr 18 2021
STATUS
approved