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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A233930 Primes p that give record exponents of 2 in p^2 - 1 (A091282). 2
3, 7, 17, 31, 127, 257, 3583, 5119, 6143, 8191, 65537, 131071, 524287, 7340033, 14680063, 104857601, 109051903, 167772161, 469762049, 2013265921, 2147483647, 21474836479, 51539607551, 206158430209, 824633720831, 2748779069441, 6597069766657, 26388279066623 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Among these terms, we find the first Mersenne primes (A000668), and some Fermat numbers (A000215).

LINKS

Hiroaki Yamanouchi, Table of n, a(n) for n = 1..100

EXAMPLE

3^2 - 1 = 8 = 2^3. 5 does not beat this record with 5^2 - 1 = 24 = 2^3 * 3.

7^2 - 1 = 48 = 2^4 * 3, so 7 sets the next record, which stands through 11 and 13.

17^2 - 1 = 288 = 2^5 * 3^2.

PROG

(PARI) lista(nn) = {r = 0; forprime (n=1, nn, v = valuation(n^2-1, 2); if (v > r, r = v; print1(n, ", "))); }

CROSSREFS

Sequence in context: A099983 A275631 A048860 * A292447 A176690 A295089

Adjacent sequences:  A233927 A233928 A233929 * A233931 A233932 A233933

KEYWORD

nonn

AUTHOR

Michel Marcus, Dec 20 2013

EXTENSIONS

a(22)-a(28) from Hiroaki Yamanouchi, Sep 27 2014

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 September 16 06:38 EDT 2019. Contains 327090 sequences. (Running on oeis4.)