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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

a(n)=15 -> (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 A260079

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

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Last modified February 25 20:04 EST 2020. Contains 332258 sequences. (Running on oeis4.)