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Search: id:A105148
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| A105148 |
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Number of semiprimes k such that k is a multiple of 3 and n^3 < k <= (n+1)^3. |
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+0
2
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| 0, 1, 3, 4, 5, 7, 10, 9, 14, 14, 19, 19, 24, 27, 32, 30, 41, 36, 44, 47, 55, 56, 62, 64, 69, 78, 77, 85, 90, 95, 107, 103, 109, 122, 118, 138, 133, 149, 142, 157, 168, 171, 177, 178, 193, 201, 214, 211, 220, 231, 243, 241, 253, 262, 272, 294, 288, 286, 308, 322
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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a(n)>=1 because there is always a 3*prime(i) between n^3 and (n+1)^3 for n>0.
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EXAMPLE
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a(3)=3 because 2^3 and 3^3 there are three 3*prime(i): 3*prime(2)=3*3,
3*prime(4)=3*5 and 3*prime(5)=3*7.
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MATHEMATICA
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f[n_] := PrimePi[Floor[n^3/3]]; Table[f[(n + 1)] - f[n], {n, 0, 60}]
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CROSSREFS
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Cf. A105149.
Sequence in context: A067526 A101760 A165713 this_sequence A072556 A047365 A048342
Adjacent sequences: A105145 A105146 A105147 this_sequence A105149 A105150 A105151
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KEYWORD
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easy,nonn
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AUTHOR
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Giovanni Teofilatto (g.teofilatto(AT)tiscalinet.it), Apr 10 2005
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EXTENSIONS
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Edited and extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Apr 16 2005
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