OFFSET
3,1
LINKS
Terrel Trotter, Normal Magic Triangles of Order n, Journal of Recreational Mathematics Vol. 5, No. 1, 1972, pp. 28-32.
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
FORMULA
O.g.f.: x^3*(12 - 13*x + 4*x^2))/(1 - x)^3.
E.g.f.: 3 + x - 2*x^2 - exp(x)*(6 - 4*x - 3*x^2)/2.
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n > 5.
a(n) = (3*n^2 + n - 6)/2 for n > 2.
MATHEMATICA
LinearRecurrence[{3, -3, 1}, {12, 23, 37}, 49]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Stefano Spezia, Feb 18 2021
STATUS
approved