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

0,1

Comments

a(62) = 1294268491, a(64) = 2300942549.

Links

Giovanni Resta, Table of n, a(n) for n = 0..91

Formula

a(n) is the prime precessing A228170(n-1).

Example

a(2) = 7 since between 7 and the next prime, 11, there are 2 semiprimes (9, 10).

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

Crossrefs

Cf. A133478, A228170.

Sequence in context: A156313 A163075 A265113 * A089359 A239892 A267487

Adjacent sequences: A228168 A228169 A228170 * A228172 A228173 A228174

Keyword

nonn

Author

Jack Brennen, Jonathan Vos Post, Zak Seidov, and Robert G. Wilson v, Aug 14 2013

Status

approved