OFFSET
0,2
COMMENTS
The terms a(5), a(6), a(7) were found by tabu search, with strong numerical evidence for the optimality of a(7).
A known lower bound for the next term a(8) is 154665569137423060000.
Upper bounds for higher terms can be found by the method described by O. Gasper, H. Pfoertner and M. Sigg, and are given in A180127, e.g., a(8) <= 154715716383037989022.
An improved lower bound is a(8) >= 154671943501236284416, provided in a private communication by Richard Gosiorovsky. - Hugo Pfoertner, Aug 27 2021
LINKS
Ortwin Gasper, Hugo Pfoertner and Markus Sigg, An Upper Bound for the Determinant of a Matrix with given Entry Sum and Square Sum JIPAM, Vol. 10, Iss. 3, Art. 63, 2008
Markus Sigg, Gasper's determinant theorem, revisited, arXiv:1804.02897 [math.CO]
EXAMPLE
a(2) = 29:
. 7 3
. 2 5
a(3) = 6640:
. 23 11 5
. 3 17 13
. 7 2 19
a(4) = 4868296:
. 53 11 23 13
. 17 47 29 3
. 7 5 43 37
. 19 31 2 41
a(5) = 5725998504
. 89 41 23 2 53
. 31 97 29 47 11
. 59 13 79 61 7
. 37 19 5 83 67
. 3 43 71 17 73
a(6) = 11305600374272:
. 137 73 7 89 83 13
. 79 139 67 19 3 97
. 101 5 149 61 37 53
. 2 109 103 71 113 11
. 59 29 41 17 131 127
. 23 47 43 151 31 107
a(7) = 35954639671827332:
. 227 71 173 43 83 29 73
. 151 163 5 181 2 103 89
. 31 223 139 61 137 97 13
. 23 47 157 211 109 19 131
. 113 7 67 127 167 199 17
. 53 79 149 37 11 193 179
. 101 107 3 41 191 59 197
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Hugo Pfoertner, Aug 11 2010
EXTENSIONS
a(7) corrected, based on private communication from Richard Gosiorovsky by Hugo Pfoertner, Aug 27 2021
a(0)=1 prepended by Alois P. Heinz, Jan 19 2022
STATUS
approved