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A136196 Numbers n such that n and n+2 are consecutive semiprimes. 7
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.

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: A189347 A248558 A198384 * A222960 A061100 A147803

Adjacent sequences:  A136193 A136194 A136195 * A136197 A136198 A136199

KEYWORD

nonn

AUTHOR

Zak Seidov, Dec 21 2007

STATUS

approved

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Last modified May 26 09:12 EDT 2017. Contains 287093 sequences.