A304456
Least semiprime of a run of exactly n even semiprimes.
Original entry on oeis.org
22, 4, 454, 300746, 111614, 14491726, 1096669582, 42205941082, 85933755478, 746001905114, 39682041123518
Offset: 1
a(1) = 22 since it is the first occurrence of a single even semiprime;
a(2) = 4 since 4 is the first of two consecutive even semiprimes in the sequence of semiprimes;
a(3) = 454 since it is the first of three consecutive even semiprimes in the sequence of semiprimes; etc.
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SplitBy[ Select[ Range@ 100, PrimeOmega@# == 2 &], Mod[#, 2] &] (* to view the runs of semiprimes of the same parity *)
A304458
Least semiprime of a run of exactly n with alternating parity.
Original entry on oeis.org
4, 14, 6, 622, 93, 1211, 69, 15746, 1273, 844147, 21, 3786374, 1357511, 37008721, 20028781, 201010021, 91186105, 6969801571, 224163661, 518479039339, 15633784177, 8191197319811, 83460915203, 669094978066, 691286884697
Offset: 1
a(1) = 4 since it is the first occurrence of a semiprime that is not part of a run of two or more semiprimes;
a(2) = 14 since it is the first of a run of exactly two consecutive semiprimes of alternating parity;
a(3) = 6 since 6 is the first of a run of exactly three consecutive semiprimes of alternating parity; etc.
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Table[ SelectFirst[ Split[ Select[ Range@ 10000000, PrimeOmega@# == 2 &], Mod[#1, 2] != Mod[#2, 2] &], Length@# == n &][[1]], {n, 13}]
Showing 1-2 of 2 results.
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