A176300 - OEIS

A176300

Numbers k such that the k-th semiprime + k is prime.

1, 5, 21, 26, 27, 28, 33, 41, 45, 48, 66, 68, 74, 86, 90, 108, 111, 112, 140, 144, 146, 149, 156, 160, 166, 183, 184, 189, 192, 210, 212, 216, 225, 228, 231, 240, 265, 268, 278, 280, 299, 300, 301, 312, 314, 325, 333, 344, 360, 363, 366, 368, 370, 378, 384, 390

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

OFFSET

1,2

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

EXAMPLE

1 is a term because A001358(1) + 1 = 5 (prime);

5 is a term because A001358(5) + 5 = 19 (prime).

MAPLE

isA001358 := proc(n) numtheory[bigomega](n) = 2 ; end proc:

A001358 := proc(n) option remember ; if n = 1 then return 4 ; else for a from procname(n-1)+1 do if isA001358(a) then return a; end if; end do; end if; end proc:

for n from 1 to 900 do if isprime(n+A001358(n)) then printf("%d, ", n) ; end if; end do: # R. J. Mathar, Apr 20 2010

MATHEMATICA

Module[{nn=2000, semi}, semi=Select[Range[nn], PrimeOmega[#]==2&]; Transpose[ Select[ Thread[{semi, Range[Length[semi]]}], PrimeQ[Total[#]]&]][[2]]] (* Harvey P. Dale, Jun 16 2016 *)

CROSSREFS

Cf. A001358 (semiprimes).

Cf. A176241.

Sequence in context: A195959 A228141 A268527 * A042319 A302305 A351325

Adjacent sequences: A176297 A176298 A176299 * A176301 A176302 A176303

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Apr 14 2010

EXTENSIONS

Corrected (68 inserted, 156 inserted) by R. J. Mathar, Apr 20 2010

STATUS

approved