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Search: id:A126782
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| A126782 |
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Primes of the form [n! mod (n!!+1)]/2, with n>=1. |
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| 3, 17, 29, 281, 254993, 690953, 607435538171963, 19213379438060803150599120087308383950505413675145269627742483783945563256960711\ 7048950195313
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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n=6 n!=720 n!!=48 [n! mod (n!!+1)]/2 = (720 mod 49)/2 = 34/2 = 17
n=7 n!=5040 n!!=105 [n! mod (n!!+1)]/2 = (5040 mod 106)/2 = 58/2 = 29
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MAPLE
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P:=proc(n) local i, j, k, w; for i from 2 by 1 to n do k:=i; w:=i-2; while w>0 do k:=k*w; w:=w-2; od; j:=(i! mod (k+1))/2; if isprime(j) then print(j); fi; od; end: P(1000);
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CROSSREFS
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Cf. A055490.
Sequence in context: A105411 A107158 A152529 this_sequence A090648 A031024 A045437
Adjacent sequences: A126779 A126780 A126781 this_sequence A126783 A126784 A126785
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KEYWORD
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hard,nonn
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AUTHOR
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Paolo P. Lava & Giorgio Balzarotti (ppl(AT)spl.at), Mar 14 2007
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