login
A194999
Number of lower triangles of a 3 X 3 0..n array with each element differing from all of its horizontal and vertical neighbors by one.
1
2, 20, 42, 66, 90, 114, 138, 162, 186, 210, 234, 258, 282, 306, 330, 354, 378, 402, 426, 450, 474, 498, 522, 546, 570, 594, 618, 642, 666, 690, 714, 738, 762, 786, 810, 834, 858, 882, 906, 930, 954, 978, 1002, 1026, 1050, 1074, 1098, 1122, 1146, 1170, 1194, 1218
OFFSET
1,1
COMMENTS
Row 3 of A194998.
LINKS
FORMULA
Empirical: a(n) = 24*n - 30 for n>2.
Empirical g.f.: 2*x*(1 + 8*x + 2*x^2 + x^3) / (1 - x)^2. - Colin Barker, May 06 2018
EXAMPLE
Some solutions for n=4:
..2......0......4......1......2......1......4......2......3......1......4
..3.2....1.2....3.2....2.1....1.2....2.3....3.4....1.2....4.3....2.3....3.2
..4.3.4..2.1.0..4.3.4..3.2.3..0.1.2..3.2.3..2.3.4..0.1.0..3.2.1..3.2.1..2.1.0
CROSSREFS
Cf. A194998.
Sequence in context: A269669 A293930 A357485 * A280436 A266842 A254542
KEYWORD
nonn
AUTHOR
R. H. Hardin, Sep 07 2011
STATUS
approved