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A271314 Largest prime factor of the n-th Jacobsthal number, A001045(n). 1
3, 5, 11, 7, 43, 17, 19, 31, 683, 13, 2731, 127, 331, 257, 43691, 73, 174763, 41, 5419, 683, 2796203, 241, 4051, 8191, 87211, 127, 3033169, 331, 715827883, 65537, 20857, 131071, 86171, 109, 25781083, 524287, 22366891, 61681, 8831418697, 5419, 2932031007403, 2113, 18837001 (list; graph; refs; listen; history; text; internal format)
OFFSET

3,1

COMMENTS

a(22) = 683 is the first repeated term in this sequence. Note that a(n+2) = A129738(n), for n < 20.

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 3..988

EXAMPLE

a(6) = 7 because A001045(6) = 21 = 3*7.

MATHEMATICA

FactorInteger[#][[-1, 1]] & /@ Take[#, -(Length@ # - 3)] &@ CoefficientList[Series[x/(1 - x - 2 x^2), {x, 0, 45}], x] (* Michael De Vlieger, Apr 04 2016, after Robert G. Wilson v at A001045 *)

PROG

(PARI) a001045(n) = (2^n - (-1)^n) / 3;

a(n) = vecmax(factor(a001045(n))[, 1]);

CROSSREFS

Essentially a combination of A005420 and A002587.

Cf. A001045, A060385, A129738, A264137.

Sequence in context: A300783 A287939 A129738 * A292006 A105603 A264987

Adjacent sequences:  A271311 A271312 A271313 * A271315 A271316 A271317

KEYWORD

nonn

AUTHOR

Altug Alkan, Apr 03 2016

STATUS

approved

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Last modified August 3 19:54 EDT 2021. Contains 346441 sequences. (Running on oeis4.)