A057158 Numerator of Sum_{k<=n} P(k)/p(k), where p(k) (resp. P(k)) is smallest (resp. largest) prime divisor of k.

1, 2, 3, 4, 5, 13, 15, 17, 19, 12, 13, 29, 31, 19, 62, 65, 68, 145, 151, 83, 30, 71, 73, 38, 39, 91, 93, 50, 51, 107, 109, 111, 355, 203, 1036, 2117, 2147, 1216, 427, 879, 889, 462, 467, 989, 3017, 1681, 1696, 3437, 3467, 1771, 1856, 3907, 3937

Offset

1,2

References

Handbook of Number Theory, D. S. Mitrinovic et al., Kluwer, Section IV.1(2).

Links

Table of n, a(n) for n=1..53.

Example

Sequence begins 1, 2, 3, 4, 5, 13/2, 15/2, 17/2, 19/2, 12, 13, 29/2, ...

Prog

(PARI) a(n) = numerator(sum(k=1, n, f = factor(k)[, 1]; if (#f, vecmax(f)/vecmin(f), 1))); \\ Michel Marcus, Feb 19 2016

Crossrefs

Cf. A057155, A020639, A006530.

Sequence in context: A039039 A141484 A175303 * A138986 A306294 A098552

Adjacent sequences: A057155 A057156 A057157 * A057159 A057160 A057161

Keyword

nonn,frac,easy

Author

N. J. A. Sloane, Sep 13 2000

Extensions

Name corrected by Michel Marcus, Feb 19 2016

Status

approved