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A087964
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a(n) is the least prime p such that exponent of highest power of 2 dividing 3p+1 equals n.
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1
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3, 17, 13, 5, 53, 149, 1237, 1109, 853, 2389, 3413, 17749, 128341, 70997, 251221, 415061, 218453, 2708821, 27088213, 29709653, 3495253, 85284181, 13981013, 39146837, 794121557, 1498764629, 492131669, 626349397, 13779686741
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OFFSET
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1,1
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LINKS
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FORMULA
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EXAMPLE
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p = 218453 is the first prime so that 3*p+1 = 655360 = (2^18)*5 has 18 as exponent of 2 in 3p+1, thus a(18) = 218453.
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MAPLE
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f:= proc(n)
local m, t, p;
t:= 2^n;
for m from 1 + 4*(n mod 2) by 6 do
p:= (t*m-1)/3;
if isprime(p) then return p fi
od
end proc:
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MATHEMATICA
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a[n_] := Module[{m, t = 2^n, p}, For[m = 1 + 4 Mod[n, 2], True, m += 6, p = (t m - 1)/3; If[PrimeQ[p], Return[p]]]];
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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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