A105148 Number of semiprimes k such that k is a multiple of 3 and n^3 < k <= (n+1)^3.

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

Offset

0,3

Comments

a(n)>=1 because there is always a 3*prime(i) between n^3 and (n+1)^3 for n>0.

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Example

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.

Mathematica

f[n_] := PrimePi[Floor[n^3/3]]; Table[f[(n + 1)] - f[n], {n, 0, 60}]

Crossrefs

Cf. A105149.

Sequence in context: A067526 A101760 A165713 * A370862 A072556 A047365

Adjacent sequences: A105145 A105146 A105147 * A105149 A105150 A105151

Keyword

easy,nonn

Author

Giovanni Teofilatto, Apr 10 2005

Extensions

Edited and extended by Ray Chandler, Apr 16 2005

Status

approved