OFFSET
0,3
COMMENTS
For n = (2k+1)^2 + (2k)^2, a(n) = k+1 and a(m) > k+1 for m > n.
This is a beautiful exploration of symmetry for the elementary classroom.
A "child" is any polyomino formed by adjoining a cell at any edge. - N. J. A. Sloane, Mar 10 2015
Optimal polyominoes have at least fourfold symmetry. - Charlie Neder, Mar 03 2019
FORMULA
From Charlie Neder, Mar 03 2019: (Start)
a(4k) >= b, where b is the least integer such that b(2b-1) >= k.
a(4k+1) = c, where c is the least integer such that (c-1)(2c-1) >= k. (End)
EXAMPLE
a(7) = 3 because this polyomino has only three children:
xx xxx xx xx
xxx has children xxx xxxx xxx
xx xx xx xxx
a(8) = 3 because of this polyomino:
xxxx
xxxx
a(9) = 2 because of this polyomino:
xxx
xxx
xxx
a(10) = 3 because of this polyomino (not the 2*5 rectangle):
xx
xxx
xxx
xx
a(11) = 4 because of this polyomino:
xxx
xxxxx
xxx
a(12) = 2 because of this polyomino:
xx
xxxx
xxxx
xx
a(13) = 2 because of the following polyomino. This will be the last time 2 will be encountered in the sequence (see comments above):
x
xxx
xxxxx
xxx
x
a(14) = 4 because of this polyomino:
xxx
xxxx
xxxx
xxx
a(15) = 4 because of this polyomino:
xx
xxxx
xxx
xxxx
xx
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Gordon Hamilton, Mar 09 2015
EXTENSIONS
a(16)-a(36) from Charlie Neder, Mar 03 2019
STATUS
approved