%I #21 May 23 2021 03:06:43

%S 1,3,21,585,69905,34636833,69810262081,567382630219905,

%T 18519084246547628289,2422583247133816584929793,

%U 1268889750375080065623288448001,2659754699919401766201267083003561985,22306191045953951743035482794815064402563073,748380193317489370459454048174977015562807531282433

%N a(n) is the number of relations from an n-element set into a set of at most n elements.

%C Symmetrically, also the number of relations from a set of at most n elements into an n-element set.

%F a(n) = (2^(n+n^2) - 1)/(2^n - 1) for n > 0 and a(0) = 1.

%F a(n) ~ 2^(n^2).

%F a(n) = A275779(n) + 1. - _Hugo Pfoertner_, May 14 2021

%t Join[{1},Table[(2^(n+n^2)-1)/(2^n-1),{n,13}]]

%Y Row sums of A344110.

%Y Cf. A000079, A002416, A031971, A089072, A117401, A275779.

%K nonn

%O 0,2

%A _Stefano Spezia_, May 13 2021