A136196 - OEIS

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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

(list; graph; refs; listen; history; text; internal format)

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