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

 

Logo

Many excellent designs for a new banner were submitted. We will use the best of them in rotation.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A077791 Palindromic wing primes (a.k.a. near-repdigit palindromes) of the form (10^a(n)-1)/9+7*10^[ a(n)/2 ]. 1
3, 9, 13, 15, 769, 1333, 1351, 6331 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Prime versus probable prime status and proofs are given in the author's table.

REFERENCES

C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.

LINKS

Table of n, a(n) for n=1..8.

Patrick De Geest, World!Of Numbers, Palindromic Wing Primes (PWP's)

Makoto Kamada, Prime numbers of the form 11...11811...11

Index entries for primes involving repunits.

FORMULA

a(n) = 2*A107648(n)+1.

EXAMPLE

a(n)=13 -> (10^13-1)/9+7*10^6 = 1111118111111.

MATHEMATICA

Do[ If[ PrimeQ[(10^n + 63*10^Floor[n/2] - 1)/9], Print[n]], {n, 3, 6400, 2}] (from Robert G. Wilson v, Dec 16 2005)

CROSSREFS

Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187.

Sequence in context: A111230 A046865 A063791 * A176393 A240108 A163595

Adjacent sequences:  A077788 A077789 A077790 * A077792 A077793 A077794

KEYWORD

more,nonn,base

AUTHOR

Patrick De Geest, Nov 16 2002.

STATUS

approved

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

Content is available under The OEIS End-User License Agreement .

Last modified April 24 19:08 EDT 2014. Contains 240988 sequences.