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 A181739 Smallest semiprime with internal digits = n; or 0 if no such number exists. 1
 106, 111, 121, 133, 141, 155, 161, 177, 183, 194, 1101, 1111, 1121, 1133, 1141, 1154, 1165, 1174, 1186, 1191, 1202, 1211, 1226, 1234, 1241, 1253, 1261, 1271, 1282, 1293, 1306, 1313, 1322, 1333, 1343, 1351, 1363, 1371, 1382, 1391, 1401, 1411, 2426 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS This is to A069691 as semiprimes A001358 are to primes A000040. 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. The smallest n such that a(n) = 0 is 20056492. - Donovan Johnson, Feb 01 2011 If one or more digits are allowed on both sides of n, the smallest semiprime containing 20056492 is 10200564926 = 2*5100282463. LINKS Alois P. Heinz, Table of n, a(n) for n = 0..10000 EXAMPLE a(23) = 1234 = 2 * 617 has the embedded substring 1"23"4. MAPLE a:= proc(n) local i, j, k; for i to 9 do for j to 9 do k:= parse(cat(i, n, j)); if not isprime(k) and add(t[2], t=ifactors(k)[2])=2 then return k fi od od; return 0; end: seq(a(n), n=0..60); # Alois P. Heinz, Feb 01 2011 CROSSREFS Cf. A001358, A032734, A069691. Sequence in context: A234966 A104315 A338602 * A178314 A010339 A277605 Adjacent sequences: A181736 A181737 A181738 * A181740 A181741 A181742 KEYWORD nonn,base AUTHOR Jonathan Vos Post, Jan 31 2011 EXTENSIONS More terms from Alois P. Heinz, Feb 01 2011 STATUS approved

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Last modified June 13 17:15 EDT 2024. Contains 373391 sequences. (Running on oeis4.)