A046720 Subsequence of beastly primes (A186086) that are palindromes that begin and end with 7.

76667, 700666007, 700000666000007, 70000006660000007

Offset

1,1

Comments

Next term is 7_{0}^48_666_{0}^48_7, containing 101 digits, and is too large to include here.

The number of digits in the terms is 2*A186521(n)+3: 5, 9, 15, 17, 101, 1159, 1589, 2647, 2787, 4787, 6135, 26961 (some correspond to probable primes)). - Jens Kruse Andersen, Jul 13 2014

Links

Jens Kruse Andersen, Table of n, a(n) for n = 1..7

R. Ondrejka, The Top Ten: a Catalogue of Primal Configurations

Tony Padilla and Brady Haran, The Most Evil Number, Numberphile video (2018)

Formula

a(n) = (7*10^(k+2)+666)*10^k+7, where k = A186521(n). - Jens Kruse Andersen, Jul 13 2014

Mathematica

Select[Table[(7*10^(n + 2) + 666)*10^n + 7, {n, 7}], PrimeQ] (* Arkadiusz Wesolowski, Sep 08 2011 *)

Crossrefs

Cf. A051003, A131645, A186086, A186521.

Sequence in context: A236709 A104327 A357608 * A258606 A152498 A237747

Adjacent sequences: A046717 A046718 A046719 * A046721 A046722 A046723

Keyword

base,nonn

Author

G. L. Honaker, Jr.

Extensions

Definition revised by N. J. A. Sloane, Feb 14 2011

Status

approved