OFFSET
0,3
LINKS
Firdous Ahmad Mala, Counting Transitive Relations with Two Ordered Pairs, Journal of Applied Mathematics and Computation, 5(4), 247-251.
Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1).
FORMULA
a(n) = 5*C(n,2) + 12*C(n,3) + 12*C(n,4).
a(n) = (1/2)*(n^4 - 2*n^3 + 4*n^2 - 3).
a(n) = A336535(n) - 1.
EXAMPLE
a(2) = 5. The five relations on a 2-set are {(1,1),(1,2)}, {(1,1),(2,1)}, {(1,1),(2,2)}, {(1,2),(2,2)} and {(2,1),(2,2)}.
MATHEMATICA
LinearRecurrence[{5, -10, 10, -5, 1}, {0, 0, 5, 27, 90}, 50] (* Harvey P. Dale, Oct 23 2022 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Firdous Ahmad Mala, Dec 05 2021
STATUS
approved