OFFSET
1,2
COMMENTS
Partial sums of number of inequivalent ways of choosing n squares from an n X n board, considering rotations and reflections to be the same.The subsequence of primes in this partial sum (unexpectedly dense at first) begins: 3, 19, 271, 251429, no more through a(20) yet 4 of the first 5 values after a(1).
FORMULA
a(n) = SUM[i=1..n] A019318(i) = SUM[i=1..n] {number of inequivalent ways of choosing i squares from an i X i board, considering rotations and reflections to be the same}.
EXAMPLE
a(6) = 1 + 2 + 16 + 252 + 6814 + 244344 = 251429 is prime.
CROSSREFS
KEYWORD
nonn
AUTHOR
Jonathan Vos Post, Feb 25 2010
STATUS
approved