A105148 - OEIS

%I #12 Jan 20 2018 22:24:10

%S 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,

%T 78,77,85,90,95,107,103,109,122,118,138,133,149,142,157,168,171,177,

%U 178,193,201,214,211,220,231,243,241,253,262,272,294,288,286,308,322

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

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

%H Vincenzo Librandi, <a href="/A105148/b105148.txt">Table of n, a(n) for n = 0..1000</a>

%e 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.

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

%Y Cf. A105149.

%K easy,nonn

%O 0,3

%A _Giovanni Teofilatto_, Apr 10 2005

%E Edited and extended by _Ray Chandler_, Apr 16 2005