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A225220 Number of lattice paths without interior points from {n}^4 to {0}^4 using steps that decrement one component by 1.

%I A225220 #7 Sep 09 2016 14:09:14
%S A225220 1,24,1944,132000,8059800,471369024,27141228576,1557898303104,
%T A225220 89658680843160,5186780199744000,301901643282754944,
%U A225220 17682835350047107968,1041936263500353390624,61736371470508652400000,3676501723843796568912000,219941299213693627194432000
%N A225220 Number of lattice paths without interior points from {n}^4 to {0}^4 using steps that decrement one component by 1.
%C A225220 An interior point p = (p_1, ..., p_4) has 4 components with 0<p_i<n for 1<=i<=4.
%H A225220 Alois P. Heinz, <a href="/A225220/b225220.txt">Table of n, a(n) for n = 0..100</a>
%p A225220 b:= proc(n, l) b(n, l):= `if`(l[4]=0, 1, `if`(l[1]>0 and l[4]<n, 0,
%p A225220        add(`if`(l[i]=0, 0, b(n, sort(subsop(i=l[i]-1, l)))), i=1..4)))
%p A225220     end:
%p A225220 a:= n-> b(n, [n$4]):
%p A225220 seq(a(n), n=0..20);
%Y A225220 Column k=4 of A225094.
%K A225220 nonn
%O A225220 0,2
%A A225220 _Alois P. Heinz_, May 02 2013