A247558 Smallest integer x > 0 such that the number of semiprimes in the interval (x/2, x] equals n.

4, 6, 10, 15, 25, 26, 35, 38, 39, 57, 58, 62, 65, 86, 87, 91, 94, 95, 121, 122, 123, 134, 142, 143, 145, 146, 159, 161, 169, 202, 203, 205, 206, 209, 214, 215, 217, 218, 219, 221, 262, 265, 278, 299, 301, 302, 303, 305, 309, 326, 327, 329, 335, 341, 346, 361, 362, 365, 382, 386, 393, 394, 395, 398

Offset

1,1

Comments

Analogous to A080359: the Labos Elemer primes.

Links

Jens Kruse Andersen, Table of n, a(n) for n = 1..10000

Example

a(6) = 26 because in the interval, (13, 26], {14, 15, 21, 22, 25, 26} are six semiprimes.

Mathematica

SemiPrimeQ[n_] := PrimeOmega[n] == 2; mx = 1000; t = Table[0, {mx + 1}]; s = 0; Do[ If[ SemiPrimeQ[k], s++]; If[ SemiPrimeQ[k/2], s--]; If[s <= mx && t[[s + 1]] == 0, t[[s + 1]] = k], {k, 8*mx}]; Rest[t]

Crossrefs

Cf. A001358, A072000, A080359.

Sequence in context: A219047 A116996 A004399 * A339115 A217836 A215232

Adjacent sequences: A247555 A247556 A247557 * A247559 A247560 A247561

Keyword

nonn

Author

Jonathan Vos Post and Robert G. Wilson v, Sep 19 2014

Status

approved