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%I #47 Jul 06 2024 21:13:24
%S 0,2,8,4,4,0,4,6,8,8,0,8,2,6,6,0,6,4,2,2,0,2,8,4,4,0,4,6,8,8,0,8,2,6,
%T 6,0,6,4,2,2,0,2,8,4,4,0,4,6,8,8,0,8,2,6,6,0,6,4,2,2,0,2,8,4,4,0,4,6,
%U 8,8,0,8,2,6,6,0,6,4,2,2,0,2,8,4,4,0,4,6,8,8,0,8,2,6,6,0,6,4,2,2
%N Last digit of n*2^n.
%C Periodic with period 20: [0,2,8,4,4,0,4,6,8,8,0,8,2,6,6,0,6,4,2,2].
%H <a href="/index/Rec#order_13">Index entries for linear recurrences with constant coefficients</a>, signature (0,1,0,-1,1,1,-1,-1,1,0,-1,0,1).
%F a(n) = A010879(A036289(n)).
%F a(n) = A373099(n) - 1.
%F a(n) = A373100(n) + 1 (n >= 1).
%F a(n) = 0 if n mod 5 = 0,
%F 2 if n mod 20 = {1, 12, 18, 19},
%F 8 if n mod 20 = {2, 8, 9, 11},
%F 4 if n mod 20 = {3, 4, 6, 17},
%F 6 if n mod 20 = {7, 13, 14, 16}.
%p a:= n-> n*2&^n mod 10:
%p seq(a(n), n=0..100);
%t a[n_] := Mod[n*2^n, 10]
%o (Python)
%o def a(n):
%o return (n * 2**n) % 10
%o (PARI) a(n,b=10) = lift(n*Mod(2,b)^n) \\ _Hugo Pfoertner_, May 24 2024
%Y Cf. A010879, A036289.
%Y Cf. A373099, A373100.
%K nonn,base,easy
%O 0,2
%A _Javier Rodríguez Ríos_, May 23 2024
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