cp's OEIS Frontend

A072845 {1, 3, 7, 9} -> Mod[ {1*{1, 3, 7, 9}, 3*{1, 3, 7, 9}, 7*{1, 3, 7, 9}, 9*{1, 3, 7, 9}}, 10}.

%I A072845 #31 Jun 01 2025 23:58:31
%S A072845 1,3,7,9,1,3,7,9,3,9,1,7,7,1,9,3,9,7,3,1,1,3,7,9,3,9,1,7,7,1,9,3,9,7,
%T A072845 3,1,3,9,1,7,9,7,3,1,1,3,7,9,7,1,9,3,7,1,9,3,1,3,7,9,9,7,3,1,3,9,1,7,
%U A072845 9,7,3,1,7,1,9,3,3,9,1,7,1,3,7,9,1,3,7,9,3,9,1,7,7,1,9,3,9,7,3,1,3,9,1,7,9
%N A072845 {1, 3, 7, 9} -> Mod[ {1*{1, 3, 7, 9}, 3*{1, 3, 7, 9}, 7*{1, 3, 7, 9}, 9*{1, 3, 7, 9}}, 10}.
%C A072845 Let S(1) = {1, 3, 7, 9}, S(n) be obtained from S(n-1) via 1 -> {1, 3, 7, 9}, 3 -> {3, 9, 1, 7}, 7 -> {7, 1, 9, 3}, 9 -> {9, 7, 3, 1}, then this sequence is the concatenation of S(1), S(2), ... - _Jianing Song_, Dec 24 2022
%p A072845 S[1]:= [1,3,7,9]:
%p A072845 R:= [1=(1,3,7,9), 3 = (3,9,1,7), 7 = (7,1,9,3), 9 = (9,7,3,1)]:
%p A072845 for i from 1 to 4 do S[i+1]:= subs(R,S[i]) od:
%p A072845 seq(op(S[i]),i=1..5); # _Robert Israel_, Dec 25 2022
%t A072845 ar={1, 3, 7, 9};
%t A072845 f[x_]=Mod[ar*x, 10];
%t A072845 br=Flatten[ NestList[f, ar, 3]]
%o A072845 (PARI) lista(nn) = {my(m = [1, 3, 7, 9], v = m); for (i=1, nn, my(w = []); for (j=1, 4, for (k=1, #v, w = concat(w, m[j]*v[k] % 10););); v = w;); w;}
%o A072845 lista(3) \\ _Michel Marcus_, Jul 01 2019
%K A072845 nonn,uned,less
%O A072845 1,2
%A A072845 _Roger L. Bagula_, Jul 24 2002
%E A072845 Edited by _Robert G. Wilson v_, Jul 27 2002