cp's OEIS Frontend

A216657 Number of n-digit 7th powers.

%I A216657 #9 Mar 19 2015 20:59:29
%S A216657 2,0,1,1,2,2,2,4,6,7,11,14,20,28,39,55,75,104,145,202,280,390,541,752,
%T A216657 1045,1452,2017,2803,3895,5412,7520,10449,14519,20174,28031,38950,
%U A216657 54120,75200,104490,145188,201738,280314,389496,541202,751998,1044898,1451881
%N A216657 Number of n-digit 7th powers.
%H A216657 Alois P. Heinz, <a href="/A216657/b216657.txt">Table of n, a(n) for n = 1..1000</a>
%e A216657 a(1) = 2: 0, 1.
%e A216657 a(3) = 1: 128.
%e A216657 a(4) = 1: 2187.
%e A216657 a(5) = 2: 16384, 78125.
%e A216657 a(6) = 2: 279936, 823543.
%e A216657 a(7) = 2: 2097152, 4782969.
%e A216657 a(8) = 4: 10000000, 19487171, 35831808, 62748517.
%e A216657 a(9) = 6: 105413504, 170859375, 268435456, 410338673, 612220032, 893871739.
%p A216657 r:= proc(n, k) local b; b:= iroot(n, k); b+`if`(b^k<n, 1, 0) end:
%p A216657 a:= n-> r(10^n, 7) -r(10^(n-1), 7) +`if`(n=1, 1, 0):
%p A216657 seq(a(n), n=1..50);
%Y A216657 Column k=7 of A216653.
%K A216657 nonn,base
%O A216657 1,1
%A A216657 _Alois P. Heinz_, Sep 12 2012