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A139474 a(n) = ((2*sqrt(2) + 3)^(2^(prime(n) - 1) - 1) - (3 - 2*sqrt(2))^(2^(prime(n) - 1) - 1))/(4*sqrt(2)). 5
1, 35, 53789260175, 300027707381709879256191290532493317737977820735 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Next term a(5) has 783 decimal digits.

Conjecture of Kenneth J Ramsey from May 16 2006 (see A001109): a(n) is divisible by 2^prime(n)-1 if and only 2^prime(n)-1 is a Mersenne prime.

LINKS

Table of n, a(n) for n=1..4.

MATHEMATICA

Table[Expand[((2*Sqrt[2] + 3)^(2^(Prime[n] - 1) - 1) - (3 - 2*Sqrt[2])^(2^(Prime[n] - 1) - 1))/(4*Sqrt[2])], {n, 1, 10}]

CROSSREFS

Cf. A001109, A139474, A139475, A139476.

Sequence in context: A126029 A107736 A261121 * A240129 A023929 A010113

Adjacent sequences:  A139471 A139472 A139473 * A139475 A139476 A139477

KEYWORD

nonn

AUTHOR

Artur Jasinski, Apr 22 2008

STATUS

approved

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Last modified March 20 05:29 EDT 2019. Contains 321344 sequences. (Running on oeis4.)