A077793 Numbers k such that 7*(10^k - 1)/9 + 10^floor(k/2) is a palindromic wing prime (a.k.a. near-repdigit palindromic prime).

3, 7, 79, 109, 337, 481, 10657, 12319, 49351, 104455

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..10.

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

Makoto Kamada, Prime numbers of the form 77...77877...77

Index entries for primes involving repunits.

Formula

a(n) = 2*A183182(n) + 1.

Example

7 is a term because 7*(10^7 - 1)/9 + 10^3 = 7778777.

Mathematica

Do[ If[ PrimeQ[(7*10^n + 9*10^Floor[n/2] - 7)/9], Print[n]], {n, 3, 12400, 2}] (* Robert G. Wilson v, Dec 16 2005 *)

Crossrefs

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

Sequence in context: A219292 A181554 A116294 * A175236 A343763 A045974

Adjacent sequences: A077790 A077791 A077792 * A077794 A077795 A077796

Keyword

more,nonn,base

Author

Patrick De Geest, Nov 16 2002

Extensions

Name corrected by Jon E. Schoenfield, Oct 31 2018

a(9) from Robert Price, Oct 07 2023

a(10) from Robert Price, Oct 30 2023

Status

approved