A156659 - OEIS

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A156659

Characteristic function of safe primes.

0, 0, 0, 0, 0, 1, 0, 1, 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, 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, 1, 0, 0, 0, 0, 0, 0, 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 (n-1)/2 is prime then 1 else 0;` `a(A005385(n)) = 1; a(A156657(n)) = 0; a(A059456(n)) = 0.` `A156875(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, Safe prime`
	FORMULA	`a(n) = A010051(n)*A010051((n-1)/2).`
	PROG	`(Haskell)` a156659 n = fromEnum $ a010051 n == 1 && a010051 (n `div` 2) == 1 `-- Reinhard Zumkeller, Sep 18 2011`
	CROSSREFS	`A156660.` `Sequence in context: A202238 A144194 A144196 * A011671 A086483 A011667` `Adjacent sequences: A156656 A156657 A156658 * A156660 A156661 A156662`
	KEYWORD	`nonn`
	AUTHOR	`Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Feb 13 2009`

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Last modified February 14 18:09 EST 2012. Contains 205663 sequences.