

A075135


Numerator of the generalized harmonic number H(n,3,1) described below.


25



1, 5, 39, 209, 2857, 11883, 233057, 2632787, 13468239, 13739939, 433545709, 7488194853, 281072414761, 284780929571, 12393920563953, 288249495707519, 2038704876507433, 2058454144222533, 2077126179153173, 60750140156034617
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OFFSET

1,2


COMMENTS

For integers a and b, H(n,a,b) is the sum of the fractions 1/(a i + b), i = 0,1,..,n1. This database already contains six instances of generalized harmonic numbers. Partial sums of the harmonic series 1+1/2+1/3+1/4+... are given by the sequence of harmonic numbers H(n,1,1) = A001008(n) / A002805(n).
The Jeep problem gives rise to the series H(n,2,1) = A025550(n) / A025547(n). Recent additions to the database are 3 * H(n,3,1) = A074596(n) / A051536(n), 3 * H(n,3,2) = A074597(n) / A051540(n), 4 * H(n,4,1) = A074598(n) / A051539(n) and 4 * H(n,4,3) = A074637(n) / A074638(n) . The numerator of H(n,4,1) is A075136. The fractions H(n,5,1), H(n,5,2), H(n,5,3) and H(n,5,4) are in A075137A075144.
The sequence H(n,a,b) is of interest only when a and b are relatively prime. The sequence can also be computed as H(n,a,b) = (PolyGamma[n+1+b/a]  PolyGamma[1+b/a])/a. The sequence H(n,a,b) diverges for all a and b.
According to Hardy and Wright, if p is an odd prime, then p divides the numerator of the harmonic number H(p1,1,1). This result can be extended to generalized harmonic numbers: for odd integer n, let q = (n2)a + 2b. If q is prime, then q divides the numerator of H(n1,a,b). For this sequence (a=3, b=1) we conclude that 11 divides a(4), 17 divides a(6), 29 divides a(10) and 47 divides a(16).
Graham, Knuth and Patashnik define another type of generalized harmonic number as the sum of fractions 1/i^k, i=1,...,n. For k=2, the sequence of fractions is A007406(n) / A007407(n).


REFERENCES

R. L. Graham, D. E. Knuth and O. Patashnik, Concrete Mathematics. AddisonWesley, Reading, MA, 1990, p. 263, 269, 272, 297, 302, 356.
G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers, 4th ed., Oxford Univ. Press, 1971, page 88.


LINKS

Table of n, a(n) for n=1..20.
Eric Weisstein's World of Mathematics, Harmonic Series
Eric Weisstein's World of Mathematics, Harmonic Number
Eric Weisstein's World of Mathematics, Jeep Problem


EXAMPLE

a(3)=39 because 1 + 1/4 + 1/7 = 39/28.


MATHEMATICA

a=3; b=1; maxN=20; s=0; Numerator[Table[s+=1/(a n + b), {n, 0, maxN1}]]


CROSSREFS

Cf. A001008, A002805, A025550, A025547, A051536, A051539, A074637, A074638, A075136A075144.
Cf. A051540, A074596, A074597, A074598.
Cf. A007406, A007407.
Sequence in context: A064445 A123614 A218918 * A202391 A053573 A003482
Adjacent sequences: A075132 A075133 A075134 * A075136 A075137 A075138


KEYWORD

easy,frac,nonn


AUTHOR

T. D. Noe, Sep 04 2002


STATUS

approved



