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Leading digit of 7^n.
3

%I #24 Jul 15 2023 14:02:54

%S 1,7,4,3,2,1,1,8,5,4,2,1,1,9,6,4,3,2,1,1,7,5,3,2,1,1,9,6,4,3,2,1,1,7,

%T 5,3,2,1,1,9,6,4,3,2,1,1,7,5,3,2,1,1,8,6,4,3,2,1,1,7,5,3,2,1,1,8,5,4,

%U 2,2,1,1,7,4,3,2,1,1,8,5,4,2,1,1,9,6,4,3,2,1,1,8,5,3,2,1,1,9,6,4,3

%N Leading digit of 7^n.

%F a(n) = A000030(A000420(n)).

%t a[n_] := IntegerDigits[7^n][[1]]; Array[a, 100, 0] (* _Amiram Eldar_, Jul 15 2023 *)

%o (PARI) a(n) = digits(7^n)[1];

%Y Cf. A008952, A060956, A111395, A362871, A363249, A364185.

%Y Cf. A000030, A000420, A001903, A008568.

%K nonn,base,easy

%O 0,2

%A _Seiichi Manyama_, Jul 15 2023