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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A326715 Values of n for which the denominator of (Sum_{prime p | n} 1/p - 1/n) is 1. 2
1, 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 30, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

n is in the sequence iff either n = 1 or n is a prime or n is a Giuga number, by one definition of Giuga numbers A007850.

LINKS

Table of n, a(n) for n=1..55.

Wikipedia, Giuga number

FORMULA

n such that A326690(n) = 1.

EXAMPLE

a(30) = denominator(Sum_{prime p | 30} 1/p - 1/30) = denominator(1/2 + 1/3 + 1/5 - 1/30) = denominator(1/1) = 1, and 30 is a Giuga number.

MATHEMATICA

PrimeFactors[n_] := Select[Divisors[n], PrimeQ];

f[n_] := Denominator[Sum[1/p, {p, PrimeFactors[n]}] - 1/n];

Select[Range[148], f[#] == 1 &]

CROSSREFS

Cf. A007850, A326689, A326690, A326691, A326692.

Sequence in context: A201879 A327783 A319333 * A089063 A247142 A171019

Adjacent sequences:  A326711 A326712 A326713 * A326716 A326717 A326718

KEYWORD

nonn

AUTHOR

Jonathan Sondow, Jul 20 2019

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
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 15 18:59 EST 2019. Contains 329149 sequences. (Running on oeis4.)