A179206 - OEIS

This site is supported by donations to The OEIS Foundation.

A179206

Smallest index k such that prime(k)*2^n * ( prime(k)*2^n +1 )-1 is prime.

1, 1, 1, 2, 1, 4, 3, 8, 1, 5, 5, 6, 6, 5, 1, 10, 16, 3, 13, 13, 37, 7, 1, 11, 1, 8, 18, 17, 6, 5, 15, 24, 12, 1, 16, 24, 7, 3, 9, 6, 17, 3, 15, 54, 24, 5, 16, 14, 8, 32, 1, 23, 17, 1, 62, 16, 23, 94, 65, 53, 70, 20, 9, 10, 9, 50, 12, 8, 12, 19, 155, 6, 46, 12, 2, 2, 12, 72, 20, 9 (list; graph; refs; listen; history; text; internal format)

	OFFSET	`1,4`
	COMMENTS	`Define partial sums S(N) = sum_{n=1..N} n and T(N) = sum_{n=1..N} a(n). Then T(N)/S(N) -> approx 0.435 as N->infinity.`
	LINKS	`R. J. Mathar, Table of n, a(n) for n = 1..8000`
	EXAMPLE	`n=1: 22(22+1)-1=19 prime so k=1 as 2=prime(1). n=2: 22^2(22^2+1)-1=71 prime so k=1 as 2=prime(1).`
	MAPLE	`A179206 := proc(n) local k, pk; for k from 1 do pk := ithprime(k)2^n ; if isprime(pk(pk+1)-1) then return k; end if; end do: end proc:` `seq(A179206(n), n=1..80) ; # R. J. Mathar, Jul 05 2010`
	CROSSREFS	`Cf. A179205` `Sequence in context: A058354 A085930 A087207 * A074987 A128280 A182177` `Adjacent sequences: A179203 A179204 A179205 * A179207 A179208 A179209`
	KEYWORD	`nonn`
	AUTHOR	`Pierre CAMI, Jul 02 2010`
	EXTENSIONS	`More terms from R. J. Mathar, Jul 05 2010`
	STATUS	`approved`

Content is available under The OEIS End-User License Agreement .

Last modified May 24 00:43 EDT 2013. Contains 225613 sequences.