A078632 - OEIS

%I #1 May 16 2003 03:00:00

%S 0,1,2,5,6,9,10,15,18,21,22,28,29,32,35,43,44,50,51,57,60,63,64,73,76,

%T 79,84,90,91,98,99,109,112,115,118,129,130,133,136,145,146,153,154,

%U 160,166,169,170,183,186,192,195,201,202,211,214,223,226,229,230,242

%N Number of geometric subsequences of [1,...,n] with integral successive-term ratio and length > 1.

%C The number of geometric subsequences of [1,...,n] with integral successive-term ratio r and length k is floor(n/r^(k-1))(n > 0, r > 1, k > 0).

%F a(n) = sum {r > 1, j > 0} floor(n/r^j)

%e a(2): [1,2]; a(3): [1,2],[1,3]; a(4): [1,2],[1,3],[1,4],[2,4],[1,2,4]

%Y Cf. A078651.

%K nonn,easy

%O 1,3

%A Robert E. Sawyer (rs.1(AT)mindspring.com)