A077792 - OEIS

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

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A077792

Numbers k such that (10^k - 1)/3 + 5*10^floor(k/2) is a palindromic wing prime (a.k.a. near-repdigit palindromic prime).

2

3, 15, 171, 189, 547, 713, 2155, 3595, 13517, 60465

(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(11) > 2*10^5. - Robert Price, Apr 21 2016

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..10.

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

Makoto Kamada, Prime numbers of the form 33...33833...33

Index entries for primes involving repunits.

FORMULA

a(n) = 2*A183177(n) + 1.

EXAMPLE

15 is a term because (10^15 - 1)/3 + 5*10^7 = 333333383333333.

MATHEMATICA

Do[ If[ PrimeQ[(10^n + 15*10^Floor[n/2] - 1)/3], Print[n]], {n, 3, 13600, 2}] (* Robert G. Wilson v, Dec 16 2005 *)

CROSSREFS

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

Sequence in context: A153280 A132683 A059386 * A153079 A173301 A361053

Adjacent sequences: A077789 A077790 A077791 * A077793 A077794 A077795

KEYWORD

more,nonn,base

AUTHOR

Patrick De Geest, Nov 16 2002

EXTENSIONS

a(10) from Robert Price, Apr 21 2016

Name corrected by Jon E. Schoenfield, Oct 31 2018

STATUS

approved