A subset S of {1,2,…,n} is said to be packed if whenever i,j∈S the number ⌊(i+j)/2⌋ is also in S. Determine how many subsets of {1,2,…,25} are packed.

Question

Details and assumptions
i and j need not be distinct. If i=j is in the set, then clearly so is ⌊(i+j)2⌋

Answer 1

questions from "brilliant.org" will not be answered.

http://www.jiskha.com/display.cgi?id=1373375428

Answer 2

i am Clavin

Answer 3

oh, well, then -- that explains it.

Answer 4

If you were Calvin, you wouldn't need to have help, you(probably)made this question. Plus, "Clavin" is misspelled.