A020646 Least positive integer k for which 7^n divides k!.

1, 7, 14, 21, 28, 35, 42, 49, 49, 56, 63, 70, 77, 84, 91, 98, 98, 105, 112, 119, 126, 133, 140, 147, 147, 154, 161, 168, 175, 182, 189, 196, 196, 203, 210, 217, 224, 231, 238, 245, 245, 252, 259, 266, 273, 280, 287, 294, 294, 301, 308, 315, 322, 329, 336, 343, 343, 343, 350

Offset: 0

Author

David W. Wilson

Keywords

• nonn

References

• H. Ibstedt, Smarandache Primitive Numbers, Smarandache Notions Journal, Vol. 8, No. 1-2-3, 1997, 216-229.

Links

• T. D. Noe, Table of n, a(n) for n = 0..1000
• F. Smarandache, Only Problems, Not Solutions!

Crossrefs

Cf. A007843, A007844, A007845.

Programs

Mathematica

lpi[n_]:=Module[{k = 1, n7 = 7^n}, While[! Divisible[k!, n7], k++]; k]; Array[lpi,60,0] (* Harvey P. Dale, Jun 29 2017 *)

PARI

a(n) = {k = 1; while (valuation(k!, 7) < n, k++); k;} \\ Michel Marcus, Aug 19 2013