| 4, 6, 15, 10, 21, 14, 55, 33, 22, 39, 26, 85, 51, 34, 57, 38, 115, 69, 46, 203, 145, 87, 58, 93, 62, 259, 185, 111, 74, 205, 123, 82, 129, 86, 235, 141, 94, 371, 265, 159, 106, 413, 295, 177, 118, 183, 122, 469, 335, 201, 134, 355, 213, 142, 219, 146, 553, 395, 237
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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Clearly all terms are semiprimes. a(0)=prime(1)^2=4. For n>=1, a(n)=k, a squarefree semiprime, where gpf(k)-lpf(k)=A006530(k)-A020639(k)=A030173(k).
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EXAMPLE
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a(3)=2*5=10 because 5-2=3=A030173(3), where the latter terms are ordered by the increasing possible differences between two distinct primes and no smaller composite number has a difference of 3 between its least and greatest prime factors.
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CROSSREFS
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Cf. A001358, A006881, A030173, A020639, A006530.
Sequence in context: A077068 A096003 A114058 this_sequence A141667 A048753 A055719
Adjacent sequences: A135090 A135091 A135092 this_sequence A135094 A135095 A135096
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KEYWORD
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nonn
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AUTHOR
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Rick L. Shepherd (rshepherd2(AT)hotmail.com), Nov 18 2007
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