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%I #40 Nov 14 2014 09:48:46
%S 106,111,121,133,141,155,161,177,183,194,1101,1111,1121,1133,1141,
%T 1154,1165,1174,1186,1191,1202,1211,1226,1234,1241,1253,1261,1271,
%U 1282,1293,1306,1313,1322,1333,1343,1351,1363,1371,1382,1391,1401,1411,2426
%N Smallest semiprime with internal digits = n; or 0 if no such number exists.
%C This is to A069691 as semiprimes A001358 are to primes A000040.
%C By placing one digit on both sides of n (1..9 on the left and on the right) one gets 81 different numbers that might be semiprimes. If none of these numbers is a semiprime then a(n) = 0.
%C The smallest n such that a(n) = 0 is 20056492. - _Donovan Johnson_, Feb 01 2011
%C If one or more digits are allowed on both sides of n, the smallest semiprime containing 20056492 is 10200564926 = 2*5100282463.
%H Alois P. Heinz, <a href="/A181739/b181739.txt">Table of n, a(n) for n = 0..10000</a>
%e a(23) = 1234 = 2 * 617 has the embedded substring 1"23"4.
%p a:= proc(n) local i, j, k;
%p for i to 9 do
%p for j to 9 do
%p k:= parse(cat(i, n, j));
%p if not isprime(k) and add(t[2], t=ifactors(k)[2])=2
%p then return k fi
%p od
%p od; return 0;
%p end:
%p seq(a(n), n=0..60); # _Alois P. Heinz_, Feb 01 2011
%Y Cf. A001358, A032734, A069691.
%K nonn,base
%O 0,1
%A _Jonathan Vos Post_, Jan 31 2011
%E More terms from _Alois P. Heinz_, Feb 01 2011
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