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Number of non-invertible functions from {0,1}^n to {0,1}^n.
2

%I #14 Sep 08 2022 08:45:02

%S 0,2,232,16736896,18446723150919663616,

%T 1461501637330639787366751139186115801643772542976

%N Number of non-invertible functions from {0,1}^n to {0,1}^n.

%H Vincenzo Librandi, <a href="/A057157/b057157.txt">Table of n, a(n) for n = 0..10</a>

%F a(n) = (2^n)^(2^n) - (2^n)! = A057156(n) - A000722(n) = A036679(A000079(n)).

%t Table[(2^n)^(2^n) - (2^n)!, {n,0,5}] (* _G. C. Greubel_, Nov 08 2018 *)

%o (Magma) [(2^n)^(2^n)-Factorial(2^n): n in [0..5]]; // _Vincenzo Librandi_, Aug 22 2011

%o (PARI) vector(6,n,n--; (2^n)^(2^n) - (2^n)!) \\ _G. C. Greubel_, Nov 08 2018

%Y Cf. A057156, A000722, A036679, A000079.

%K nonn,easy

%O 0,2

%A _Henry Bottomley_, Aug 15 2000