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