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A131188
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Indices of products of twin primes in the semiprimes.
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0
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6, 13, 48, 103, 270, 508, 1001, 1413, 2724, 3052, 4859, 5668, 8029, 9062, 9608, 12558, 13828, 17319, 18823, 22781, 28077, 40162, 42359, 48113, 60703, 71793, 79161, 83792, 90129, 94954, 140436, 144445, 146452, 156704, 165199, 218110, 223095
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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FORMULA
| {i: A001358(i) = A001359(k) * A006512(k), for some k >0}. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 26 2007
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EXAMPLE
| sp(6)=15=3*5, sp(13)=35=5*7, sp(48)=143=11*13, sp(103)=323=17*19, sp(270)=899=29*31, sp(508)=1763=41*43, sp(1001)=3599=59*61, sp(1413)=5183=71*73; sp(n)=nth semiprime.
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CROSSREFS
| Cf. A128301.
Sequence in context: A034753 A100905 A041489 * A203977 A003757 A187985
Adjacent sequences: A131185 A131186 A131187 * A131189 A131190 A131191
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KEYWORD
| nonn
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AUTHOR
| Zak Seidov (zakseidov(AT)yahoo.com), Sep 25 2007
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EXTENSIONS
| More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 26 2007
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