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A283362
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a(n) = (floor(2*n/3))! mod (2n-1).
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1
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0, 1, 2, 2, 6, 2, 11, 0, 6, 17, 0, 1, 20, 0, 1, 2, 0, 0, 7, 0, 15, 40, 0, 41, 0, 0, 20, 0, 0, 26, 47, 0, 0, 47, 0, 18, 33, 0, 0, 42, 0, 75, 0, 0, 31, 0, 0, 0, 21, 0, 94, 9, 0, 56, 65, 0, 95, 0, 0, 0, 0, 0, 0, 99, 0, 57, 0, 0, 32, 121, 0, 0, 0, 0, 148, 64, 0, 0, 49
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OFFSET
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1,3
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COMMENTS
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if a(n) > 0 then 2n-1, except n=5 and n=13, is prime.
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LINKS
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MAPLE
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f:= proc(n)
local m, r, p, k;
m:= floor(2*n/3);
r:= 2*n-1;
p:= 1;
for k from 1 to m do
p:= p*k mod r;
if p = 0 then break fi;
od:
p
end proc:
f(1):= 0:
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MATHEMATICA
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Table[Mod[Floor[(2n)/3]!, 2n-1], {n, 80}] (* Harvey P. Dale, Aug 21 2024 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,changed
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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