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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A091859 a(1) = 2, a(n) is the least prime of the form 2k*a(n-1)+1 where 2k is the least even number not used earlier. 0
2, 5, 31, 311, 3733, 59729, 1194581, 57339889, 1605516893, 22477236503, 1933042339259, 143045133105167, 2574812395893007, 87543621460362239, 700348971682897913, 58829313621363424693, 1411903526912722192633 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..17.

EXAMPLE

a(2) = 5 = 2*2+1, But a(3) = 31 though 11= 5*2 +1 is also prime.

PROG

Contribution from Rick L. Shepherd, Sep 08 2009: (Start)

(PARI) {a=[2]; terms=1; used=Set();

while(terms<30, k2=0; until(isprime(k2*a[terms]+1),

until(setsearch(used, k2)==0, k2=k2+2));

a=concat(a, k2*a[terms]+1); terms++; used=setunion(used, Set([k2]))); a} (End)

CROSSREFS

Sequence in context: A192397 A097396 A056788 * A085873 A303289 A051048

Adjacent sequences:  A091856 A091857 A091858 * A091860 A091861 A091862

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Mar 13 2004

EXTENSIONS

a(6) onwards by Rick L. Shepherd, Sep 08 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
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 17 04:03 EDT 2019. Contains 327119 sequences. (Running on oeis4.)