A076476 Fractions a(n)/n are such that gcd(a(n),n)=1, a(n) > 0 and a(n) is as small as possible so that the partial sums of the fractions have prime numerator. Let a(1)=1.

1, 1, 1, 3, 1, 1, 1, 3, 4, 1, 5, 1, 1, 3, 1, 9, 1, 7, 4, 3, 1, 5, 1, 23, 9, 3, 10, 13, 13, 29, 7, 19, 5, 21, 2, 17, 2, 3, 7, 7, 5, 5, 6, 7, 1, 43, 3, 59, 27, 17, 4, 5, 9, 7, 1, 9, 2, 9, 7, 29, 8, 9, 4, 25, 3, 119, 2, 27, 4, 29, 4, 37, 5, 3, 2, 5, 9, 7, 10, 49, 1, 35, 12, 11, 6, 1, 22, 1, 13, 11, 4

Offset

1,4

Comments

By Dirichlet's Theorem, it is always possible to find the next term. See A076477 for the list of primes appearing in the numerator. The denominators of these sums are the same as for harmonic numbers, A002805. The sum of the fractions diverges. Is there an upper bound for a(n)/n?

Links

Table of n, a(n) for n=1..91.

Example

a(4) = 3 because 1/4 yields 1/1 + 1/2 + 1/3 + 1/4 = 25/12, but 3/4 yields 1/1 + 1/2 + 1/3 + 3/4 = 31/12.

Mathematica

nMax = 100; lst = {1}; numer = {1}; s = 1; Do[k = 1; While[GCD[k, n] > 1 || ! PrimeQ[Numerator[s + k/n]], k++ ]; s = s + k/n; AppendTo[lst, k]; AppendTo[numer, Numerator[s]]; k++, {n, 2, nMax}]; lst

Crossrefs

Cf. A076477.

Sequence in context: A069290 A365334 A348660 * A243200 A016733 A060234

Adjacent sequences: A076473 A076474 A076475 * A076477 A076478 A076479

Keyword

nonn,frac

Author

T. D. Noe, Oct 14 2002

Status

approved