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A105148
Number of semiprimes k such that k is a multiple of 3 and n^3 < k <= (n+1)^3.
2
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
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
KEYWORD
easy,nonn
AUTHOR
Giovanni Teofilatto, Apr 10 2005
EXTENSIONS
Edited and extended by Ray Chandler, Apr 16 2005
STATUS
approved