A341704 a(n) = 20*binomial(n,6) + 2*binomial(n,3) + 1.
1, 1, 1, 3, 9, 21, 61, 211, 673, 1849, 4441, 9571, 18921, 34893, 60789, 101011, 161281, 248881, 372913, 544579, 777481, 1087941, 1495341, 2022483, 2695969, 3546601, 4609801, 5926051, 7541353, 9507709, 11883621, 14734611, 18133761, 22162273, 26910049, 32476291
Offset: 0
Examples
a(7)=211 since the strings are the 140 permutations of 0001112, the 35 permutations of 0002222, the 35 permutations of 1112222, and 2222222.
Links
- Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-7,1).
Formula
E.g.f.: exp(x)*(1 + x^3/6)^2.
O.g.f.:(1 - 6*x + 15*x^2 - 18*x^3 + 9*x^4 + 19*x^6)/(1 - x)^7. - Stefano Spezia, Feb 19 2021
Comments