A228171 Least prime such that between it and the next prime there are exactly n semiprimes.
2, 3, 7, 31, 89, 139, 113, 211, 1381, 1637, 1129, 2557, 2971, 1327, 15683, 16141, 9973, 35677, 34061, 43331, 19609, 107377, 162143, 44293, 404597, 461717, 838249, 155921, 535399, 492113, 396733, 2181737, 370261, 1468277, 6034247, 3933599, 1671781, 25180171
Offset: 0
Keywords
Examples
a(2) = 7 since between 7 and the next prime, 11, there are 2 semiprimes (9, 10).
Links
- Giovanni Resta, Table of n, a(n) for n = 0..91
Programs
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Mathematica
t = Table[0, {100}]; p=3; While[p < 3100000000, q = NextPrime[p]; a = Count[ PrimeOmega[ Range[p, q]], 2]; If[ t[[a]] == 0, t[[a]] = p; Print[{p, a}]]; p = q]; t
Formula
a(n) is the prime precessing A228170(n-1).
Comments