A092696 Smoothly undulating palindromic primes of the form (12*10^n-21)/99.

1212121, 12121212121, 1212121212121212121212121212121212121212121

Offset: 1

Author

Rick L. Shepherd, Mar 04 2004

Keywords

• bref
• nonn
• base

Comments

The De Geest link calls these smoothly undulating palindromic primes. Corresponding n are given in A062209. Equivalently, primes of the form 1212...121: Decimal digits "12" repeated k times with 1 appended (or "21" repeated k times with 1 prefixed). Corresponding k are given in A056803. The next term, a(4), has "12" repeating A056803(4) = 69 times and length A062209(4) = 2*A056803(4) + 1 = 139 decimal digits.

Links

• P. De Geest, SUPP Reference Table
• Index entries for sequences related to smoothly undulating palindromic primes

Crossrefs

Cf. A056803 (number of 12's (or 21's)), A062209 (corresponding decimal digit lengths).

Cf. A032758, A033619, A030291, A059168, A242541, A004022.

Formula

a(n) = (4*10^A062209(n)-7)/33. - M. F. Hasler, Jul 30 2015

Extensions

Edited by M. F. Hasler, Jul 30 2015