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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A296444 Numbers k such that 2*10^(2k)+2*10^k+1 are prime. 1
2, 3, 6, 10, 276, 746, 1090, 1485, 6186 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers of this form divide 4*10^(4k)+1.

LINKS

Table of n, a(n) for n=1..9.

EXAMPLE

20201, 2002001, 2000002000001, and 200000000020000000001 are prime, while 221=13*17, 200020001=569*351529, and 20000200001=17*29*1129*35933.

MATHEMATICA

ParallelMap[ If[ PrimeQ[2*10^(2 #) + 2*10^# + 1], #, Nothing] &, Range@ 6500] (* Robert G. Wilson v, Dec 13 2017 *)

PROG

(PARI) isok(k) = isprime(2*10^(2*k)+2*10^k+1); \\ Michel Marcus, Dec 13 2017

CROSSREFS

See A296443 for 2*10^(2k)-2*10^k+1.

Sequence in context: A056606 A186408 A062527 * A038752 A125714 A247953

Adjacent sequences:  A296441 A296442 A296443 * A296445 A296446 A296447

KEYWORD

nonn,more

AUTHOR

Patrick A. Thomas, Dec 13 2017

EXTENSIONS

a(5)-a(6) from Michel Marcus, Dec 13 2017

a(7)-a(9) from Robert G. Wilson v, Dec 13 2017

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 June 18 07:06 EDT 2019. Contains 324203 sequences. (Running on oeis4.)