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%I A110605 #8 Oct 12 2019 12:00:25
%S A110605 4,6,7,11,12,15,16,19,20,24,25,26,34,36,40,44,47,55,57,61,64,65,66,73,
%T A110605 74,78,79,80,82,83,89,92,97,99,100,101,103,104,108,109,110,113,118,
%U A110605 124,136,137,142,145,148,149,150,152,158,162,164,167,172,173,176,181,187
%N A110605 Numbers n whose base 7 representations, interpreted as base 10 integers, are semiprimes.
%C A110605 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.
%e A110605 a(1) = 4 because 4 (base 7) = 4 (base 10) = 2 * 2, a semiprime (A001358).
%e A110605 a(2) = 6 because 6 (base 7) = 6 (base 10) = 2 * 3
%e A110605 a(3) = 7 because 7 (base 7) = 10 and 10 (base 10) = 2 * 5.
%e A110605 a(4) = 11 because 11 (base 7) = 14 and 14 (base 10) = 2 * 7.
%e A110605 a(5) = 12 because 12 (base 7) = 15 and 15 (base 10) = 3 * 5.
%t A110605 Select[Range[187], Plus @@ Last /@ FactorInteger[FromDigits[IntegerDigits[ #, 7]]] == 2 &] (* _Ray Chandler_, Aug 05 2005 *)
%Y A110605 Cf. A001358, A007093, A108873, A110602, A110603, A110604, A110606, A110607.
%K A110605 base,easy,nonn
%O A110605 1,1
%A A110605 _Jonathan Vos Post_, Jul 30 2005
%E A110605 Extended by _Ray Chandler_, Aug 05 2005

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