login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A108820 Primes such that the outer 2 digits are n and n+1 and all inner digits are 3, where 0 < n < 9. 1
233, 839, 2333, 6337, 23333, 63337, 83339, 633337, 6333337, 8333333339, 23333333333, 63333333337, 83333333339, 63333333333337, 8333333333333339, 23333333333333333, 23333333333333333333333 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The first digit of each term must be 2, 6, or 8. - Harvey P. Dale, Jun 13 2020

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..40

FORMULA

a(x) = 10^(x+1)*n+floor(10^x*3/9)*10+n+1. Output if a(x) is prime.

MATHEMATICA

Select[Sort[Flatten[Table[10FromDigits[PadRight[{i}, n, 3]]+i+1, {i, {2, 6, 8}}, {n, 2, 25}]]], PrimeQ] (* Harvey P. Dale, Jun 13 2020 *)

PROG

(PARI) n10np1(n) = { local(x, y, k); for(x=1, n, for(k=1, 8, y=10^(x+1)*k+floor(10^x*3/9)*10+k+1; if(isprime(y), print1(y", ")) ) ) }

CROSSREFS

Sequence in context: A142783 A142848 A023338 * A230392 A003537 A037033

Adjacent sequences:  A108817 A108818 A108819 * A108821 A108822 A108823

KEYWORD

easy,nonn,base

AUTHOR

Cino Hilliard, Jul 11 2005

EXTENSIONS

Corrected by T. D. Noe, Nov 15 2006

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified August 9 06:42 EDT 2022. Contains 356017 sequences. (Running on oeis4.)