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A191013 Largest k such that (2^n-k)*2^n-k is a prime number. 0
1, 5, 9, 29, 61, 119, 249, 507, 1017, 2045, 4047, 8181, 16381, 32765, 65521, 131069, 262137, 524277, 1048567, 2097145, 4194285, 8388597, 16777185, 33554421, 67108821, 134217725, 268435405, 536870909, 1073741811, 2147483619, 4294967275, 8589934569, 17179869177 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,2

LINKS

Table of n, a(n) for n=2..34.

EXAMPLE

a(2)=1 because (2^2-1)*2^2-1 = 11 is prime,

a(3)=5 because (2^3-5)*2^3-5 = 19 is prime,

a(4)=7 because (2^4-7)*2^4-7 = 137 is prime.

PROG

(PARI) a(n)=forstep(k=2^n-1, 1, -1, ispseudoprime((2^n-k)*2^n-k) & return(k)) \\ M. F. Hasler, Jun 17 2011

CROSSREFS

Cf. A000040.

Sequence in context: A303676 A163779 A280487 * A193487 A006131 A352008

Adjacent sequences: A191010 A191011 A191012 * A191014 A191015 A191016

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Jun 16 2011

STATUS

approved

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Last modified February 5 09:25 EST 2023. Contains 360084 sequences. (Running on oeis4.)