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 A190664 Least semiprime whose prime factors differ by 2*prime(n). 1
 21, 55, 39, 51, 203, 87, 111, 123, 371, 183, 335, 395, 623, 267, 291, 327, 1703, 635, 411, 1043, 447, 815, 1211, 543, 591, 7223, 1055, 2951, 1115, 687, 771, 1883, 831, 843, 4043, 1535, 951, 1655, 1011, 1047, 12059, 1835, 2723, 1167, 1191, 1203, 4763, 1347 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS FORMULA a(n) = A073703(n) * A073704(n). EXAMPLE a(5) = 203 because 203 = 7*29, and 29 - 7 = 22 = 2*11 = 2*prime(5). MATHEMATICA f[n_] := Block[{p=3}, While[! PrimeQ[p+2*Prime[n]], p=NextPrime[p]]; p*(p+2*Prime[n])]; Table[f[n], {n, 1, 60}] CROSSREFS Cf. A073703, A073704. Sequence in context: A304517 A007796 A211460 * A144302 A180674 A067431 Adjacent sequences:  A190661 A190662 A190663 * A190665 A190666 A190667 KEYWORD nonn AUTHOR Michel Lagneau, May 16 2011 STATUS approved

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Last modified January 29 01:40 EST 2020. Contains 331328 sequences. (Running on oeis4.)