A089890 Number of subsets of {1,.., n} containing exactly two squares.

0, 0, 0, 4, 8, 16, 32, 64, 192, 384, 768, 1536, 3072, 6144, 12288, 24576, 49152, 98304, 196608, 393216, 786432, 1572864, 3145728, 6291456, 10485760, 20971520, 41943040, 83886080, 167772160, 335544320, 671088640, 1342177280

Offset

1,4

Comments

a(n) = A000217(A000196(n)-1)*A089887(n);

for n>2: a(n) = A089886(n,2).

Links

Table of n, a(n) for n=1..32.

Formula

a(n) = (n^(1/2)*(n^(1/2)-1)*2^(n-n^(1/2)))/2.

Crossrefs

Cf. A089889.

Sequence in context: A147639 A049934 A328634 * A338313 A049932 A272712

Adjacent sequences: A089887 A089888 A089889 * A089891 A089892 A089893

Keyword

nonn

Author

Reinhard Zumkeller, Nov 13 2003

Status

approved