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A110607 Numbers n whose base 9 representations, interpreted as base 10 integers, are semiprimes.

%I A110607 #10 Oct 12 2019 11:59:46
%S A110607 4,6,9,13,14,19,20,23,24,30,31,32,35,42,46,50,52,53,56,59,67,70,74,77,
%T A110607 78,79,87,91,95,98,100,101,102,111,112,118,119,120,122,123,131,134,
%U A110607 136,141,151,152,156,158,160,163,164,165,167,168,174,175,176,178,179,181
%N A110607 Numbers n whose base 9 representations, interpreted as base 10 integers, are semiprimes.
%C A110607 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.
%H A110607 Harvey P. Dale, <a href="/A110607/b110607.txt">Table of n, a(n) for n = 1..1000</a>
%e A110607 a(1) = 4 because 4 (base 9) = 4 (base 10) = 2 * 2, a semiprime (A001358).
%e A110607 a(2) = 6 because 6 (base 9) = 6 (base 10) = 2 * 3.
%e A110607 a(3) = 9 because 9 (base 9) = 10 and 10 (base 10) = 2 * 5.
%e A110607 a(4) = 13 because 13 (base 9) = 14 and 14 (base 10) = 2 * 7.
%e A110607 a(5) = 14 because 14 (base 9) = 15 and 15 (base 10) = 3 * 5.
%t A110607 Select[Range[181], Plus @@ Last /@ FactorInteger[FromDigits[IntegerDigits[ #, 9]]] == 2 &] (* _Ray Chandler_, Aug 05 2005 *)
%t A110607 Select[Range[200],PrimeOmega[FromDigits[IntegerDigits[#,9]]]==2&] (* _Harvey P. Dale_, Dec 02 2018 *)
%Y A110607 Cf. A001358, A007095, A108873, A110602, A110603, A110604, A110605, A110607.
%K A110607 base,easy,nonn
%O A110607 1,1
%A A110607 _Jonathan Vos Post_, Jul 30 2005
%E A110607 Extended by _Ray Chandler_, Aug 05 2005