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

Author

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

Keywords

• nonn

Comments

Analogous to A080359: the Labos Elemer primes.

Examples

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

Links

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

Crossrefs

Cf. A001358, A072000, A080359.

Programs

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]