A242677 Semiprimes whose binary representation, read in decimal, is also semiprime.
15, 33, 55, 57, 65, 69, 77, 87, 115, 121, 129, 143, 169, 205, 209, 265, 299, 305, 321, 339, 361, 415, 417, 447, 451, 481, 493, 505, 517, 519, 535, 551, 553, 581, 611, 623, 667, 687, 695, 721, 737, 779, 789, 799, 865, 871, 893, 901, 905, 923, 943, 949, 955, 973
Offset: 1
Examples
a(2) = 33 = 3 * 11 is semiprime. Binary representation of 33 = 100001 = 11 * 9091 which is also semiprime. a(4) = 57 = 3 * 19 is semiprime. Binary representation of 57 = 111001 = 11 * 10091 which is also semiprime.
Links
- K. D. Bajpai, Table of n, a(n) for n = 1..10000