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A104296
a(n) = prime((a(n)-1)/2), a(1)=9.
3
9, 11, 13, 17, 23, 37, 67, 139, 349, 1039, 3727, 16007, 81853, 492059, 3436987, 27605857, 252391267, 2602897093, 30034790941, 384953881369, 5444681375227, 84482367674813
OFFSET
1,1
COMMENTS
All primes except a(1) which is any odd integer; a(1)=9 is first a(1) giving nontrivial sequence: three cases a(1)=3,5,7 give a(n)=a(1); other a(1)'s A104297-A104304.
MATHEMATICA
a[1] = 9; a[n_] := a[n] = Prime[(a[n - 1] + 1)/2]; Table[ a[n], {n, 22}] (* Robert G. Wilson v, Mar 24 2005 *)
KEYWORD
easy,nonn
AUTHOR
Zak Seidov, Feb 28 2005
EXTENSIONS
a(14) - a(22) from Robert G. Wilson v, Mar 24 2005
STATUS
approved