A380662 Numbers m such that Sum_{k>=0} floor(m/5^k) is prime.

2, 3, 6, 11, 16, 25, 30, 34, 35, 39, 44, 49, 58, 68, 73, 79, 82, 84, 87, 89, 92, 103, 106, 111, 113, 121, 123, 126, 131, 146, 154, 155, 159, 160, 170, 183, 188, 193, 202, 207, 212, 217, 219, 224, 226, 228, 236, 248, 251, 266, 271, 279, 280, 284, 289, 295

Offset

1,1

Links

Table of n, a(n) for n=1..56.

Example

floor(16/1) + floor(16/5) = 19, so 16 is in the sequence.

Mathematica

f[n_] := Sum[Floor[(n-1)/5^k], {k, 0, Floor[Log[5, n]]}]  (* A191610 *)
Select[Range[400], PrimeQ[f[#]] &]

Crossrefs

Cf. A191610, A381239.

Sequence in context: A210458 A228864 A289434 * A049794 A034031 A121617

Adjacent sequences: A380657 A380658 A380659 * A380663 A380664 A380665

Keyword

nonn,new

Author

Clark Kimberling, Feb 19 2025

Status

approved