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Search: id:A128301
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| A128301 |
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Indices of squares (of primes) in the semiprimes. |
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+0
3
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| 1, 3, 9, 17, 40, 56, 90, 114, 164, 253, 289, 404, 484, 533, 634, 783, 973, 1031, 1233, 1373, 1452, 1683, 1842, 2112, 2483, 2676, 2779, 2995, 3108, 3320, 4124, 4384, 4775, 4926, 5593, 5741, 6172, 6644, 6962, 7448, 7955, 8108, 8978, 9147, 9512, 9697, 10842
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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A001358(a(n)) = A001248(n) = A000040(n)^2.
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EXAMPLE
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a(4) = 17 as 49 = 7^2 = prime(4)^2, the fourth square in the semiprimes, is the seventeenth semiprime.
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PROGRAM
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perl -MMath::Pari=factorint, PARI -wle 'my $c = 0; my $s = PARI 1; while (1) { ++$s; my($sp, $si) = @{factorint($s)}; next if @$sp > 2; next if $si->[0] + (@$si > 1 ? $si->[1] : 0) != 2; ++$c; print "$s => $c" if @$sp == 1}' (from Hugo van der Sanden (hv(AT)crypt.org), Sep 25 2007)
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CROSSREFS
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Cf. A128302, A001358, A001248.
Sequence in context: A123325 A116688 A011755 this_sequence A018307 A108050 A009211
Adjacent sequences: A128298 A128299 A128300 this_sequence A128302 A128303 A128304
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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), Feb 25 2007
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