OFFSET
3,2
REFERENCES
Christoph Gerber, "Zum Abzahlen semimagischer Quadrate" [Apparently unpublished. - R. J. Mathar, Nov 13 2011]
P. A. MacMahon, Combinatory Analysis, Vol II; Chelsea, New York, 1960.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 3..1000
Christoph Gerber, More information [?Broken link]
Index entries for linear recurrences with constant coefficients, signature (3,-2,-2,4,-4,2,2,-3,1).
FORMULA
a(n) = 1/64*n^4-1/32*n^3+1/32*n^2+d*n+e with: d:=-1/8 if n=0 or n=2 (mod 4) d:=3/32 if n=1 or n=3 (mod 4) e:=0 if n=0 (mod 4) e:=-7/64 if n=1 (mod 4) e:=1/8 if n=2 (mod 4) e:=1/64 if n=3 (mod 4).
G.f.: -x^3*(1-x+3*x^2-x^3+x^4) / ( (1+x^2)*(1+x)^2*(x-1)^5 ). - R. J. Mathar, Nov 13 2011
a(n) = (2*n*(n-1)*(n^2-n+1)-7*(2*n-1)*(-1)^n-8*(-1)^((2*n-1+(-1)^n)/4)+1)/128. - Luce ETIENNE, Oct 29 2017
EXAMPLE
a(4)=2 because there are 2 essentially different semi-magic squares of order 3 with semi-magic sum 4: [1,1,2; 1,2,1; 2,1,1] and [1,1,2; 2,1,1; 1,2,1].
MAPLE
A131292:=proc(n) local d, e: if (n mod 4) in {0, 2} then d:=-1/8 fi: if (n mod 4) in {1, 3} then d:=3/32 fi: if (n mod 4) in {0} then e:=0 fi: if (n mod 4) in {1} then e:=-7/64 fi: if (n mod 4) in {2} then e:=1/8 fi: if (n mod 4) in {3} then e:=1/64 fi: return 1/64*n^4-1/32*n^3+1/32*n^2+d*n+e: end proc:
MATHEMATICA
LinearRecurrence[{3, -2, -2, 4, -4, 2, 2, -3, 1}, {1, 2, 7, 14, 29, 49, 83, 127, 192}, 50] (* Harvey P. Dale, Jan 26 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Christoph Gerber (christoph.gerber(AT)phbern.ch), Jun 25 2007
STATUS
approved