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A087964 a(n) is the least prime p such that exponent of highest power of 2 dividing 3p+1 equals n. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = A000040(Min{x; A007814(1 + 3*A000040(x)) = n}).

EXAMPLE

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.

MAPLE

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:

map(f, [$1..100]); # Robert Israel, Nov 18 2017

MATHEMATICA

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]]]];

Array[a, 100] (* Jean-François Alcover, Aug 28 2020, after Robert Israel *)

CROSSREFS

Cf. A087272, A087273, A087274, A007814, A087230, A087963.

Sequence in context: A088122 A273702 A273710 * A174182 A120448 A095422

Adjacent sequences:  A087961 A087962 A087963 * A087965 A087966 A087967

KEYWORD

nonn

AUTHOR

Labos Elemer, Sep 18 2003

EXTENSIONS

More terms from Ray Chandler, Sep 21 2003

STATUS

approved

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Last modified December 3 08:07 EST 2021. Contains 349445 sequences. (Running on oeis4.)