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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A212487 Smallest k > 0 such that (5^n+k)*5^n-1 and (5^n+k)*5^n+1 are a twin prime pair. 2
1, 17, 85, 47, 19, 71, 955, 815, 223, 269, 607, 1619, 2737, 53, 883, 1319, 2797, 4757, 1585, 1535, 295, 557, 3511, 269, 277, 5747, 2125, 53, 13345, 2195, 109, 1175, 2995, 5597, 3787, 1619, 6577, 8549, 3475, 5435, 4807, 20045, 23353, 9341, 2857, 2117, 1429, 16283, 25333, 7949 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Conjecture: there is always one such k for n > 0.

LINKS

Pierre CAMI, Table of n, a(n) for n = 1..500

FORMULA

a(n) = A082466(5^n). - R. J. Mathar, Jul 20 2012

MAPLE

A212487 := proc(n)

    local k, p ;

    for k from 1 do

        p := (5^n+k)*5^n-1 ;

        if isprime(p) and isprime(p+2) then

            return k;

        end if;

    end do:

end proc: # R. J. Mathar, Jul 20 2012

PROG

SCRIPT

DIM nn, 0

DIM kk

DIM jj

DIMS tt

OPENFILEOUT myfile, a(n).txt

OPENFILEOUT myf, b(n).txt

LABEL loopn

SET nn, nn+1

SET jj, 0

IF nn>500 THEN END

SET kk, -1

LABEL loopk

SET kk, kk+2

SETS tt, %d, %d\,; nn; kk

PRP (5^nn+kk)*5^nn-1, tt

IF ISPRP THEN GOTO a

IF ISPRIME THEN GOTO a

GOTO loopk

LABEL a

SET jj, jj+1

PRP (5^nn+kk)*5^nn+1, tt

IF ISPRP THEN GOTO d

IF ISPRIME THEN GOTO d

GOTO loopk

LABEL d

WRITE myfile, tt

SETS tt, %d, %d\,; nn; jj

WRITE myf, tt

GOTO loopn

CROSSREFS

Cf. A212488.

Sequence in context: A213436 A239667 A156968 * A288420 A156157 A146389

Adjacent sequences:  A212484 A212485 A212486 * A212488 A212489 A212490

KEYWORD

nonn

AUTHOR

Pierre CAMI, Jul 18 2012

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 July 17 08:42 EDT 2019. Contains 325098 sequences. (Running on oeis4.)