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A176191 Numbers n such that semiprime(n)-1 is prime, where semiprime(n) is A001358. 0
1, 2, 5, 14, 22, 25, 52, 62, 88, 100, 126, 133, 142, 169, 188, 198, 202, 222, 229, 263, 299, 321, 340, 354, 359, 364, 388, 407, 426, 465, 478, 504, 539, 556, 577, 579, 611, 668, 700, 722, 737, 781, 797, 814, 857, 905, 916, 932, 984, 1033, 1108, 1118, 1148 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..53.

EXAMPLE

a(1)=1 because semiprime(1)-1=3=prime, a(2)=2 because semiprime(2)-1=5=prime, a(3)=5 because semiprime(5)-1=13=prime.

MATHEMATICA

nn=5000; With[{sps=Select[Range[nn], PrimeOmega[#]==2&]}, Transpose[ Select[ Thread[ {sps, Range[ Length[sps]]}], PrimeQ[First[#]-1]&]][[2]]] (* Harvey P. Dale, Jul 19 2011 *)

CROSSREFS

Cf. A174838.

Sequence in context: A228958 A216669 A015633 * A265248 A131661 A321287

Adjacent sequences:  A176188 A176189 A176190 * A176192 A176193 A176194

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Apr 11 2010

EXTENSIONS

Corrected (478 inserted) by R. J. Mathar, Apr 13 2010

STATUS

approved

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Last modified July 4 12:18 EDT 2020. Contains 335448 sequences. (Running on oeis4.)