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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A077783 Numbers k such that (10^k-1)/9 + 4*10^floor(k/2) is a palindromic wing prime (a.k.a. near-repdigit palindrome). 1
3, 15, 91, 231, 1363, 2497, 4963, 5379, 12397, 26395, 120253 (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(12) > 2*10^5. - Robert Price, 12 Oct 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..11.

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

Makoto Kamada, Prime numbers of the form 11...11511...11

Index entries for primes involving repunits.

FORMULA

a(n) = 2*A107125(n) + 1.

EXAMPLE

a(n) = 15 -> (10^15 - 1)/9 + 4*10^7 = 111111151111111.

MATHEMATICA

Do[ If[ PrimeQ[(10^n + 36*10^Floor[n/2] - 1)/9], Print[n]], {n, 3, 26400, 2}] (* Robert G. Wilson v, Dec 16 2005 *)

PROG

(MAGMA) [n: n in [3..2000 by 2] | IsPrime((10^n+36*10^Floor(n div 2)-1) div 9)]; // Vincenzo Librandi, Oct 13 2015

CROSSREFS

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

Sequence in context: A185369 A024339 A034954 * A047019 A099251 A171790

Adjacent sequences:  A077780 A077781 A077782 * A077784 A077785 A077786

KEYWORD

more,nonn,base

AUTHOR

Patrick De Geest, Nov 16 2002

EXTENSIONS

a(11) from Robert Price, Oct 12 2015

Name edited by Jon E. Schoenfield, Oct 13 2015

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 21:16 EDT 2017. Contains 292391 sequences.