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Search: id:A105120
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| A105120 |
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a(1) = 2; k(1) = 0; for n > 1: k(n) = smallest number j >= k(n-1) such that 2*a(n-1) + j is prime; a(n) = 2*a(n-1) + k(n). |
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2
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| 2, 5, 11, 23, 47, 97, 197, 397, 797, 1597, 3203, 6421, 12889, 25841, 51749, 103567, 207227, 414553, 829211, 1658533, 3317177, 6634469, 13269059, 26538257, 53076679, 106153547, 212307299, 424614829, 849229907, 1698460067, 3396920419
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Numbers k(n) are given in A105121.
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LINKS
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Robert G. Wilson v, Table of n, a(n) for n = 1..3000..
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EXAMPLE
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a(10) = 1597; k(10) = 3; 2*1597 + j is not prime for 3 <= j < 9, but 2*1597 + 9
= 3203 is prime. Hence k(11) = 9 and a(11) = 3203.
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MATHEMATICA
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a[1] = {2, 0}; a[n_] := a[n] = Block[{m = 2a[n - 1][[1]], k = a[n - 1][[2]]}, While[ !PrimeQ[m + k], k++ ]; {m + k, k}]; Table[ a[n][[1]], {n, 30}] (from Robert G. Wilson v (rgwv(AT)rgwv.com), Apr 08 2005)
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PROGRAM
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(PARI) print1(a=2, ", "); k=0; for(n=2, 31, j=k; while(!isprime(2*a+j), j++); k=j; print1(a=2*a+k, ", ")) (Brockhaus)
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CROSSREFS
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k(n) is in A105121.
Sequence in context: A083329 A081973 A055496 this_sequence A084403 A055011 A007505
Adjacent sequences: A105117 A105118 A105119 this_sequence A105121 A105122 A105123
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KEYWORD
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nonn
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AUTHOR
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Yasutoshi Kohmoto (zbi74583(AT)boat.zero.ad.jp), Apr 08 2005
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EXTENSIONS
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Edited, corrected and extended by Klaus Brockhaus (klaus-brockhaus(AT)t-online.de) and Robert G. Wilson v (rgwv(AT)rgwv.com), Apr 08 2005
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