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A176300 Numbers k such that the k-th semiprime + k is prime. 1
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
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
KEYWORD
nonn
AUTHOR
EXTENSIONS
Corrected (68 inserted, 156 inserted) by R. J. Mathar, Apr 20 2010
STATUS
approved

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Last modified March 29 08:13 EDT 2024. Contains 371265 sequences. (Running on oeis4.)