A279798 Largest prime factor of 78557*2^n + 1.

67, 104743, 8609, 281, 521, 1163, 1436471, 12391, 136343, 1483, 23663, 727, 10453, 2029, 135481883, 7429021, 2059324621, 6864415403, 3716857, 9629, 451358821, 51782483, 62504399, 439322585771, 63337, 128110399, 42209, 59569669, 111486983, 10936129, 31585821557

Offset: 1

Author

Seiichi Manyama, Dec 19 2016

Keywords

• nonn

Comments

a(n) <= A258073(n) / A258091(n).

Examples

			78557 * 2^1 + 1 = 157115 = 5 * 7 * 67^2. So a(1) = 67.
78557 * 2^2 + 1 = 314229 = 3 * 104743. So a(2) = 104743.
		

Links

• Daniel Suteu, Table of n, a(n) for n = 1..412
• Wikipedia, Sierpinski Number

Crossrefs

Cf. A002587, A258073, A258091.

Programs

Mathematica

Table[FactorInteger[2^n * 78557 + 1][[-1, 1]], {n, 30}] (* Alonso del Arte, Jan 01 2017 *)

PARI

a(n) = my(k=78557*2^n+1); factor(k)[omega(k), 1] \\ Felix Fröhlich, Jan 01 2017

Formula

a(n) = A006530(A258073(n)).