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 A110605 Numbers n whose base 7 representations, interpreted as base 10 integers, are semiprimes. 6
 4, 6, 7, 11, 12, 15, 16, 19, 20, 24, 25, 26, 34, 36, 40, 44, 47, 55, 57, 61, 64, 65, 66, 73, 74, 78, 79, 80, 82, 83, 89, 92, 97, 99, 100, 101, 103, 104, 108, 109, 110, 113, 118, 124, 136, 137, 142, 145, 148, 149, 150, 152, 158, 162, 164, 167, 172, 173, 176, 181, 187 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A108873 is the equivalent using base 3. A110602 is the equivalent using base 4. A110603 is the equivalent using base 5. A110604 is the equivalent using base 6. A110606 is the equivalent using base 8. A110607 is the equivalent using base 9. LINKS EXAMPLE a(1) = 4 because 4 (base 7) = 4 (base 10) = 2 * 2, a semiprime (A001358). a(2) = 6 because 6 (base 7) = 6 (base 10) = 2 * 3 a(3) = 7 because 7 (base 7) = 10 and 10 (base 10) = 2 * 5. a(4) = 11 because 11 (base 7) = 14 and 14 (base 10) = 2 * 7. a(5) = 12 because 12 (base 7) = 15 and 15 (base 10) = 3 * 5. MATHEMATICA Select[Range, Plus @@ Last /@ FactorInteger[FromDigits[IntegerDigits[ #, 7]]] == 2 &] (* Ray Chandler, Aug 05 2005 *) CROSSREFS Cf. A001358, A007093, A108873, A110602, A110603, A110604, A110606, A110607. Sequence in context: A039590 A134038 A247546 * A206775 A287157 A102140 Adjacent sequences:  A110602 A110603 A110604 * A110606 A110607 A110608 KEYWORD base,easy,nonn AUTHOR Jonathan Vos Post, Jul 30 2005 EXTENSIONS Extended by Ray Chandler, Aug 05 2005 STATUS approved

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Last modified July 30 18:40 EDT 2021. Contains 346359 sequences. (Running on oeis4.)