OFFSET
1,2
COMMENTS
Powers of seventh root of 10 rounded up.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = ceiling(10^((n-1)/7)).
EXAMPLE
1^7 = 1 has 1 digit, 2^7 = 128 has three digits, hence a(2) = a(3) = 2.
MATHEMATICA
Table[(Ceiling[10^((n - 1)/7)]), {n, 1, 60}] (* Vincenzo Librandi, Sep 20 2013 *)
PROG
(Magma) [Ceiling(Root(10^(n-1), 7)): n in [1..44]];
(Python)
from sympy import integer_nthroot
def A130081(n): return (lambda x:x[0]+(not x[1]))(integer_nthroot(10**(n-1), 7)) # Chai Wah Wu, Jun 20 2024
CROSSREFS
Cf. A011276, A011557 (powers of 10), A017936 (smallest number whose square has n digits), A018005 (smallest number whose cube has n digits), A018074 (smallest number whose fourth power has n digits), A018143 (smallest number whose fifth power has n digits), A130080 to A130084 (smallest number whose sixth ... tenth power has n digits).
KEYWORD
nonn,base,easy
AUTHOR
Klaus Brockhaus, May 07 2007
STATUS
approved