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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.)