id:A105149 - OEIS Search Results

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Number of even semiprimes k such that n^2 < k <= (n+1)^2.

+0
2

0, 1, 1, 2, 1, 2, 2, 2, 1, 3, 2, 3, 3, 2, 4, 2, 3, 3, 4, 5, 1, 6, 3, 5, 3, 4, 4, 5, 4, 6, 5, 5, 3, 6, 5, 7, 6, 4, 6, 5, 7, 6, 5, 6, 6, 8, 8, 5, 6, 8, 7, 6, 5, 9, 9, 7, 10, 6, 7, 8, 5, 10, 6, 10, 9, 8, 8, 10, 8, 11, 5, 9, 9, 13, 10, 9, 9, 9, 8, 8, 10, 12, 7, 11, 12, 12, 10, 10, 12, 10, 12, 10, 10, 10, 11 (list; graph; listen)

	OFFSET	`0,4`
	COMMENT	`a(n)>=1 because there is always a number 2*prime(i) between n^2 and (n+1)^2 for n>0.`
	EXAMPLE	`a(6)=2 because between 5^2 and 6^2 there are two 2prime(i): 2prime(6)=213 and 2prime(7)=2*17.`
	MATHEMATICA	`f[n_] := PrimePi[Floor[n^2/2]]; Table[f[(n + 1)] - f[n], {n, 0, 100}]`
	CROSSREFS	`Cf. A105148.` `Sequence in context: A023588 A001227 A060764 this_sequence A068307 A158946 A023645` `Adjacent sequences: A105146 A105147 A105148 this_sequence A105150 A105151 A105152`
	KEYWORD	`easy,nonn`
	AUTHOR	`Giovanni Teofilatto (g.teofilatto(AT)tiscalinet.it), Apr 10 2005`
	EXTENSIONS	`Edited and extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Apr 16 2005`

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Last modified November 30 13:13 EST 2009. Contains 167758 sequences.

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