login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual Appeal: Please make a donation (tax deductible in USA) to keep the OEIS running. Over 5000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A134411 a(n) is the smallest positive integer such that the numerator of (Sum_{k=1..n} 1/a(k)) is prime (or 1), for all positive integers n. 4
1, 1, 1, 2, 3, 1, 3, 1, 1, 2, 6, 1, 1, 2, 4, 1, 1, 1, 3, 1, 1, 2, 3, 1, 2, 3, 2, 1, 4, 6, 1, 3, 1, 3, 2, 8, 3, 2, 3, 3, 1, 2, 6, 2, 1, 3, 3, 1, 5, 4, 3, 2, 1, 3, 1, 4, 2, 1, 3, 2, 1, 3, 1, 1, 3, 1, 1, 2, 6, 2, 4, 5, 3, 1, 3, 2, 1, 3, 3, 1, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

Table of n, a(n) for n=1..81.

EXAMPLE

The sum of the reciprocals of the first 9 terms is 1 + 1 + 1 + 1/2 + 1/3 + 1 + 1/3 + 1 + 1 = 43/6. (And the numerator, 43, is prime.) Adding the reciprocal of 1 to this gets 49/6 (in reduced form). But 49 is composite. However, adding the reciprocal of 2 to 43/6 gets 23/3 (when written in reduced form). 23 is a prime, so therefore a(10) = 2.

MATHEMATICA

a = {1}; s = 1; Do[i = 1; While[ ! PrimeQ[Numerator[s + 1/i]], i++ ]; s = s + 1/i; AppendTo[a, i], {80}]; a (* Stefan Steinerberger, Oct 27 2007 *)

CROSSREFS

Cf. A134412, A134413.

Sequence in context: A082503 A190549 A064442 * A126044 A114899 A220906

Adjacent sequences:  A134408 A134409 A134410 * A134412 A134413 A134414

KEYWORD

nonn

AUTHOR

Leroy Quet, Oct 24 2007

EXTENSIONS

More terms from Stefan Steinerberger, Oct 27 2007

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified December 11 03:18 EST 2016. Contains 279034 sequences.