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A108839
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a(1) = 1; a(n) = number of previous terms a(k) such that a(k) + n is prime.
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3
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1, 1, 0, 2, 2, 2, 1, 0, 3, 4, 5, 4, 4, 2, 7, 5, 6, 5, 5, 1, 4, 5, 3, 6, 6, 7, 8, 6, 7, 7, 6, 5, 5, 6, 11, 16, 13, 9, 9, 11, 12, 13, 7, 4, 6, 11, 10, 12, 8, 7, 8, 12, 12, 15, 17, 14, 12, 11, 15, 16, 15, 14, 11, 13, 16, 21, 22, 18, 12, 11, 16, 17, 14, 12, 12, 12, 20, 17, 10, 8, 14, 14, 16, 13, 21
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OFFSET
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1,4
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LINKS
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EXAMPLE
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Among the first 10 terms, a(3) + 11, a(4) + 11, a(5) + 11, a(6) + 11 and a(8) + 11 are primes. So a(11) = 5.
If we add 10 to each of the first 9 terms of the sequence, we get [11,11,10,12,12, 12,11,10,13]. Of these, only the three 11's and the 13 are primes. So a(10) = 4.
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MAPLE
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A108839 := proc(nmax) local a, nxt, k ; n := 2 ; a := [1] ; while n < nmax do nxt := 0 ; for k from 1 to n-1 do if isprime(op(k, a)+n) then nxt := nxt+1 ; fi ; od ; a := [op(a), nxt] ; n := n+1 ; od ; a ; end: A108839(80) ; # R. J. Mathar, Aug 11 2008
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MATHEMATICA
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t={1}; Do[AppendTo[t, Length[Select[t+n, PrimeQ]]], {n, 2, 2000}]; t (* T. D. Noe *)
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PROG
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(PARI) {m=85; v=[1]; for(n=2, m, c=0; for(j=1, length(v), if(isprime(v[j]+n), c++)); v=concat(v, c)); for(j=1, m, print1(v[j], ", "))} - Klaus Brockhaus, Aug 04 2005
(Haskell)
a108839 n = a108839_list !! (n-1)
a108839_list = 1 : f 2 [1] where
f x zs = z : f (x + 1) (z : zs) where
z = toInteger $ sum $ map (a010051 . (+ x)) zs
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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