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A025711
Index of 5^n within the sequence of the numbers of the form 5^i*10^j.
1
1, 2, 4, 7, 10, 14, 19, 24, 30, 37, 44, 52, 61, 71, 81, 92, 104, 116, 129, 143, 157, 172, 188, 205, 222, 240, 259, 278, 298, 319, 340, 362, 385, 409, 433, 458, 484, 510, 537, 565, 593, 622, 652, 683, 714, 746, 779, 812, 846, 881, 916, 952, 989, 1027, 1065, 1104, 1144
OFFSET
0,2
COMMENTS
Positions of zeros in A025687. - R. J. Mathar, Jul 06 2025
LINKS
FORMULA
From Amiram Eldar, Nov 13 2025: (Start)
A025625(a(n)) = 5^n.
a(n) = 1 + Sum_{k=0..n} ceiling(k * c), where c = log_10(5) (A153268).
a(n) ~ c * n^2 / 2, where c is defined above. (End)
MATHEMATICA
Accumulate[Table[Ceiling[n * Log10[5]], {n, 0, 60}]] + 1 (* Amiram Eldar, Nov 13 2025 *)
CROSSREFS
KEYWORD
nonn,easy
EXTENSIONS
Offset corrected by Amiram Eldar, Nov 13 2025
STATUS
approved