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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A077787 Palindromic wing primes (a.k.a. near-repdigit palindromes) of the form (10^a(n)-1)/9+5*10^[ a(n)/2 ]. 1
21, 29, 81, 119, 321, 825, 1121, 2579, 3693 (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.

a(10) > 2*10^5. - Robert Price, Sep 28 2015

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..9.

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

Makoto Kamada, Prime numbers of the form 11...11611...11

Index entries for primes involving repunits.

FORMULA

a(n) = 2*A107126(n)+1.

EXAMPLE

a(n)=21 -> (10^21-1)/9+5*10^10 = 111111111161111111111.

MATHEMATICA

Do[ If[ PrimeQ[(10^n + 45*10^Floor[n/2] - 1)/9], Print[n]], {n, 3, 4000, 2}] (* Robert G. Wilson v, Dec 16 2005 *)

CROSSREFS

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

Sequence in context: A004196 A211253 A209975 * A039372 A043195 A043975

Adjacent sequences:  A077784 A077785 A077786 * A077788 A077789 A077790

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 | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified September 23 20:33 EDT 2017. Contains 292391 sequences.