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A216657
Number of n-digit 7th powers.
2
2, 0, 1, 1, 2, 2, 2, 4, 6, 7, 11, 14, 20, 28, 39, 55, 75, 104, 145, 202, 280, 390, 541, 752, 1045, 1452, 2017, 2803, 3895, 5412, 7520, 10449, 14519, 20174, 28031, 38950, 54120, 75200, 104490, 145188, 201738, 280314, 389496, 541202, 751998, 1044898, 1451881
OFFSET
1,1
LINKS
EXAMPLE
a(1) = 2: 0, 1.
a(3) = 1: 128.
a(4) = 1: 2187.
a(5) = 2: 16384, 78125.
a(6) = 2: 279936, 823543.
a(7) = 2: 2097152, 4782969.
a(8) = 4: 10000000, 19487171, 35831808, 62748517.
a(9) = 6: 105413504, 170859375, 268435456, 410338673, 612220032, 893871739.
MAPLE
r:= proc(n, k) local b; b:= iroot(n, k); b+`if`(b^k<n, 1, 0) end:
a:= n-> r(10^n, 7) -r(10^(n-1), 7) +`if`(n=1, 1, 0):
seq(a(n), n=1..50);
CROSSREFS
Column k=7 of A216653.
Sequence in context: A353945 A089614 A064875 * A328614 A257511 A039802
KEYWORD
nonn,base
AUTHOR
Alois P. Heinz, Sep 12 2012
STATUS
approved