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A156321
a(1)=0, a(n+1) is smallest nonprime > 2*a(n).
1
0, 1, 4, 9, 20, 42, 85, 171, 343, 687, 1375, 2751, 5504, 11009, 22019, 44039, 88080, 176162, 352325, 704651, 1409303, 2818607, 5637215, 11274431, 22548863, 45097727, 90195455, 180390911, 360781823, 721563647, 1443127295, 2886254591
OFFSET
1,3
LINKS
EXAMPLE
a(5) is the smallest nonprime > 2*a(4)=2*9=18, hence a(5)=20.
MATHEMATICA
np[n_]:=Module[{k=2n+1}, If[PrimeQ[k], k+1, k]]; NestList[np, 0, 40] (* Harvey P. Dale, May 23 2012 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from R. J. Mathar, Feb 10 2009
STATUS
approved