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A165769
Largest prime factor of the semiprime 2^A165767(n)-A165767(n).
4
29, 11, 4679, 131063, 123817, 318949, 209510599, 49977801259, 2199023255531, 9334079, 7250118529, 2305843009213693921, 17457916757373919459, 27748320404471, 717308900550128276543, 2028240960365167042394725128581, 221537999297485978817301176713390723
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
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
Sequence in context: A336061 A160494 A332940 * A040815 A033349 A088400
KEYWORD
nonn
AUTHOR
M. F. Hasler, Oct 08 2009
STATUS
approved