|
|
A261177
|
|
Maximum value of (1/2)*Sum_{i=1..n} Sum_{j=1..n} Sum_{k=1..n} Sum_{l=1..n} gcd(b(i,j),b(k,l)) * ((i-k)^2+(j-l)^2) for an n X n matrix b filled with the integers 1 to n^2.
|
|
1
|
|
|
0, 10, 180, 1392, 6149, 21350, 57192, 137617, 298864, 593378, 1101739, 1936342, 3216080
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
Best results found in Al Zimmermann's Programming Contest "Delacorte Numbers". For more information see A261176. All terms beyond a(5) are conjectured based on numerical results. Terms up to a(11) have at least 5 independent verifications. Lower bounds for the next terms are a(14)>=5189492, a(15)>=8110781, a(16)>=12239616, a(17)>=18073562, a(18)>=26055061, a(19)>=36769303, a(20)>=51095165.
|
|
LINKS
|
|
|
EXAMPLE
|
a(3)=180, because no arrangement of the matrix elements exists that produces a larger Delacorte Number than e.g. ((2 3 4)(9 1 5)(8 7 6)).
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,hard
|
|
AUTHOR
|
|
|
EXTENSIONS
|
Lower bounds for a(18) and a(20) improved by Hugo Pfoertner, Nov 22 2015
|
|
STATUS
|
approved
|
|
|
|