A165769 - OEIS

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A165769

Largest prime factor of the semiprime 2^A165767(n)-A165767(n).

29, 11, 4679, 131063, 123817, 318949, 209510599, 49977801259, 2199023255531, 9334079, 7250118529, 2305843009213693921, 17457916757373919459, 27748320404471, 717308900550128276543, 2028240960365167042394725128581, 221537999297485978817301176713390723

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OFFSET

1,1

COMMENTS

A165768(n)=2 <=> A165767(n)=2k for some k <=> a(n)=4^k/2-k is prime. This is the case for k=3,9,21,31,1125,...

LINKS

Max Alekseyev, Table of n, a(n) for n = 1..39

FORMULA

a(n)=(2^A165767(n)-A165767(n))/A165768(n).

EXAMPLE

46235097144973199564251065756966919577339221 is in this sequence because it is the largest prime factor of the semiprime 2^199-199.

CROSSREFS