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 A110607 Numbers n whose base 9 representations, interpreted as base 10 integers, are semiprimes. 7
 4, 6, 9, 13, 14, 19, 20, 23, 24, 30, 31, 32, 35, 42, 46, 50, 52, 53, 56, 59, 67, 70, 74, 77, 78, 79, 87, 91, 95, 98, 100, 101, 102, 111, 112, 118, 119, 120, 122, 123, 131, 134, 136, 141, 151, 152, 156, 158, 160, 163, 164, 165, 167, 168, 174, 175, 176, 178, 179, 181 (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. A110605 is the equivalent using base 7. A110606 is the equivalent using base 8. LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 EXAMPLE a(1) = 4 because 4 (base 9) = 4 (base 10) = 2 * 2, a semiprime (A001358). a(2) = 6 because 6 (base 9) = 6 (base 10) = 2 * 3. a(3) = 9 because 9 (base 9) = 10 and 10 (base 10) = 2 * 5. a(4) = 13 because 13 (base 9) = 14 and 14 (base 10) = 2 * 7. a(5) = 14 because 14 (base 9) = 15 and 15 (base 10) = 3 * 5. MATHEMATICA Select[Range, Plus @@ Last /@ FactorInteger[FromDigits[IntegerDigits[ #, 9]]] == 2 &] (* Ray Chandler, Aug 05 2005 *) Select[Range, PrimeOmega[FromDigits[IntegerDigits[#, 9]]]==2&] (* Harvey P. Dale, Dec 02 2018 *) CROSSREFS Cf. A001358, A007095, A108873, A110602, A110603, A110604, A110605, A110607. Sequence in context: A078782 A165897 A020165 * A085802 A084916 A187910 Adjacent sequences:  A110604 A110605 A110606 * A110608 A110609 A110610 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 29 13:28 EDT 2021. Contains 346346 sequences. (Running on oeis4.)