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A092696 Smoothly undulating palindromic primes of the form (12*10^n-21)/99. 4

%I #11 Jul 30 2015 10:17:41

%S 1212121,12121212121,1212121212121212121212121212121212121212121

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

%C 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.

%H P. De Geest, <a href="http://www.worldofnumbers.com/undulat.htm">SUPP Reference Table</a>

%H <a href="/index/Pri#pri_supp">Index entries for sequences related to smoothly undulating palindromic primes</a>

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

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

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

%K bref,nonn,base

%O 1,1

%A _Rick L. Shepherd_, Mar 04 2004

%E Edited by _M. F. Hasler_, Jul 30 2015

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Last modified March 29 04:59 EDT 2024. Contains 371264 sequences. (Running on oeis4.)