A156877 - OEIS

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A156877

Number of numbers <= n that are safe primes and also Sophie Germain primes.

0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,11`
	COMMENTS	`a(n) = A156874(n) + A156875(n) - A156876(n);` `a(n) = SUM(A156659(k)*A156660(k): 1<=k<=n).`
	LINKS	`R. Zumkeller, Table of n, a(n) for n = 1..10000`
	EXAMPLE	`a(120) = #{5, 11, 23, 83} = 4.`
	CROSSREFS	`A059455, A005384, A005385, A000720.` `Sequence in context: A057467 A074594 A001069 * A110591 A105209 A179076` `Adjacent sequences: A156874 A156875 A156876 * A156878 A156879 A156880`
	KEYWORD	`nonn`
	AUTHOR	`Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Feb 18 2009`

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Last modified February 15 15:20 EST 2012. Contains 205823 sequences.