A136196 Numbers n such that n and n+2 are consecutive semiprimes.

4, 49, 55, 91, 119, 143, 159, 183, 185, 203, 215, 219, 235, 247, 265, 287, 289, 299, 303, 319, 321, 327, 339, 391, 411, 413, 415, 451, 469, 471, 515, 517, 527, 533, 535, 543, 551, 579, 581, 589, 667, 669, 679, 685, 687, 695, 721, 753, 779, 789, 791, 813, 815

Offset

1,1

Links

Zak Seidov, Table of n, a(n) for n = 1..1000.

Example

4 and 6 are 1st and 2nd semiprimes,
49 and 51 are 17th and 18th semiprimes,
55 and 57 are 19th and 20th semiprimes.

Mathematica

Position[Partition[PrimeOmega[Range[900]], 3, 1], _?(#[[1]]==#[[3]]==2 && #[[2]]!=2&), 1, Heads->False]//Flatten (* Harvey P. Dale, Oct 15 2021 *)

Prog

(PARI) isok(n) = (bigomega(n) == 2) && (bigomega(n+2) == 2) && (bigomega(n+1) != 2); \\ Michel Marcus, Oct 13 2013

Crossrefs

Cf. A001358, A065516.

Sequence in context: A248558 A372052 A198384 * A222960 A061100 A147803

Adjacent sequences: A136193 A136194 A136195 * A136197 A136198 A136199

Keyword

nonn

Author

Zak Seidov, Dec 21 2007

Status

approved