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A105149
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Number of even semiprimes k such that n^2 < k <= (n+1)^2.
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1
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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; refs; listen; history; internal format)
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OFFSET
| 0,4
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COMMENTS
| a(n)>=1 because there is always a number 2*prime(i) between n^2 and (n+1)^2 for n>0.
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EXAMPLE
| a(6)=2 because between 5^2 and 6^2 there are two 2*prime(i): 2*prime(6)=2*13 and 2*prime(7)=2*17.
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MATHEMATICA
| f[n_] := PrimePi[Floor[n^2/2]]; Table[f[(n + 1)] - f[n], {n, 0, 100}]
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CROSSREFS
| Cf. A105148.
Sequence in context: A175242 A001227 A060764 * A068307 A158946 A023645
Adjacent sequences: A105146 A105147 A105148 * A105150 A105151 A105152
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KEYWORD
| easy,nonn
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AUTHOR
| Giovanni Teofilatto (g.teofilatto(AT)tiscalinet.it), Apr 10 2005
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EXTENSIONS
| Edited and extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Apr 16 2005
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