%I #17 Aug 20 2024 09:08:57

%S 1,4,18,136,1575,23346,411796,8388640,193710285,5000000050,

%T 142655835366,4458050224200,151437553296211,5556003412779106,

%U 218946945190429800,9223372036854775936,413620130943168382233,19673204037648268787874,989209827830156794562170,52428800000000000000000200

%N a(n) = (n^n + n^2)/2.

%e a(3) = (3^3 + 3^2)/2 = (27+9)/2 = 18.

%t a[n_]:=(n^n + n^2)/2; Array[a,20] (* _Stefano Spezia_, Aug 19 2024 *)

%o (Python) print([int((n**n+n**2)/2) for n in range(1,20)])

%Y Cf. A000290, A000312, A117694.

%K nonn,easy,changed

%O 1,2

%A _Alex Ratushnyak_, Jul 24 2012