A131200 a(2n-1) = the smallest prime not occurring earlier in the sequence. a(2n) = the a(2n-1)th prime.
2, 3, 5, 11, 7, 17, 13, 41, 19, 67, 23, 83, 29, 109, 31, 127, 37, 157, 43, 191, 47, 211, 53, 241, 59, 277, 61, 283, 71, 353, 73, 367, 79, 401, 89, 461, 97, 509, 101, 547, 103, 563, 107, 587, 113, 617, 131, 739, 137, 773, 139, 797, 149, 859, 151, 877, 163, 967, 167
Offset: 1
Keywords
Examples
The smallest prime not occurring among the first 8 terms of the sequence is 19; So a(9) = 19. The a(9)th prime = 19th prime is 67; so a(10) = 67.
Programs
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Maple
A131200 := proc(nmax) local a,i,n; a := [2] ; for n from 2 to nmax do if n mod 2 = 0 then a := [op(a),ithprime(op(-1,a))] ; else for i from 1 do if not ithprime(i) in a then a := [op(a),ithprime(i)] ; break ; fi ; od; fi ; od; a ; end: A131200(80); # R. J. Mathar, Oct 30 2007
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Mathematica
a = {}; For[n = 1, n < 65, n++, If[OddQ[n], i = 1; While[Length[Intersection[{Prime[i]}, a]] > 0, i++ ]; AppendTo[a, Prime[i]], AppendTo[a, Prime[a[[ -1]]]]]]; a (* Stefan Steinerberger, Oct 27 2007 *)
Extensions
More terms from Stefan Steinerberger and R. J. Mathar, Oct 27 2007
Comments