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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A066814 Smallest prime p such that (p-1) has n divisors, or 0 if no such prime exists. 2
2, 3, 5, 7, 17, 13, 0, 31, 37, 113, 0, 61, 0, 193, 401, 211, 65537, 181, 0, 241, 577, 13313, 0, 421, 1297, 12289, 4357, 2113, 0, 1009, 0, 1321, 25601, 2424833, 752734097, 1801, 0, 786433, 495617, 2161, 0, 4801, 0, 15361, 7057, 155189249, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The only primes p for which p-1 has a prime number of divisors are Fermat primes A019434.

LINKS

Table of n, a(n) for n=1..47.

EXAMPLE

a(17)=65537 because DivisorSigma[0,65536]=17.

MATHEMATICA

it=Table[ p=Prime[ n ]; DivisorSigma[ 0, p-1 ], {n, 400000} ]; Flatten[ Position[ it, #, 1, 1 ]&/@Range[ 100 ]/.{}- > 0 ]

CROSSREFS

Cf. A004249, A007516, A066529.

Sequence in context: A215658 A059471 A059496 * A072885 A178209 A042994

Adjacent sequences:  A066811 A066812 A066813 * A066815 A066816 A066817

KEYWORD

nonn

AUTHOR

Wouter Meeussen, Jan 20 2002

EXTENSIONS

Comment clarified by T. D. Noe, Nov 06 2009

Edited by Max Alekseyev, Nov 10 2009

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 September 26 00:10 EDT 2017. Contains 292500 sequences.