%I #17 Feb 12 2024 06:36:55

%S 1,43,1366,38410,1010815,25515421,625878268,15034586596,355440320845,

%T 8298240786655,191776931546866,4395106938053518,100020864586079851,

%U 2262634152933752305,50921433140756382520,1140878530467983299336

%N a(1)=1, a(n) = n*21^(n-1) + a(n-1).

%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (29,-224,196).

%F G.f.: x/((1 - x)*(1 - 21*x)^2). - _Stefano Spezia_, Mar 11 2020

%o (PARI) a(n) = (1+21^n*(20*n-1))/400; \\ _Jinyuan Wang_, Mar 11 2020

%K nonn,easy

%O 1,2

%A _Olivier Gérard_