A156660 - OEIS

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A156660

Characteristic function of Sophie Germain primes.

0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; internal format)

	OFFSET	`0,1`
	COMMENTS	`a(n) = if n and also 2*n+1 is prime then 1 else 0; a(A005384(n)) = 1; a(A138887(n)) = 0; a(A053176(n)) = 0.` `A156874(n) = SUM(a(k): 1<=k<=n). [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Feb 18 2009]`
	LINKS	`R. Zumkeller, Table of n, a(n) for n = 1..10000` `Index entries for characteristic functions` `Wikipedia, Sophie Germain prime`
	FORMULA	`a(n) = A010051(n)A010051(2n+1).`
	CROSSREFS	`A156659.` `Sequence in context: A175337 A132380 A021913 * A155899 A117814 A062301` `Adjacent sequences: A156657 A156658 A156659 * A156661 A156662 A156663`
	KEYWORD	`nonn`
	AUTHOR	`Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Feb 13 2009`
	EXTENSIONS	`Definition corrected by Daniel Forgues (squid(AT)zensearch.com), Aug 04 2009`

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Last modified February 16 14:37 EST 2012. Contains 205930 sequences.