%I #24 Sep 08 2022 08:45:13
%S 23,223,2223,22223,222223,2222223,22222223,222222223,2222222223,
%T 22222222223,222222222223,2222222222223,22222222222223,
%U 222222222222223,2222222222222223,22222222222222223,222222222222222223
%N Concatenation of n 2's followed by 3.
%C Sequence arising in _Farideh Firoozbakht_'s solution to Prime Puzzle 251; 23 is the only pointer prime (A089823) not containing the digit "1".
%H Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/RecursiveSequences.html">Recursive Sequences</a>
%H Carlos Rivera's Prime Puzzles and Problems Connection, <a href="http://www.primepuzzles.net/puzzles/puzz_251.htm">Puzzle 251, Pointer primes</a>
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F a(n) = (10^(n+1) - 1)/9*2 + 1.
%F a(n) = 10*a(n-1) - 7, with a(1)=23. - _Vincenzo Librandi_, Nov 16 2010
%F From _Colin Barker_, May 06 2012: (Start)
%F a(n) = 11*a(n-1) - 10*a(n-2).
%F G.f.: x*(23-30*x)/((1-x)*(1-10*x)). (End)
%o (Magma) [ n eq 1 select 23 else 10*Self(n-1)-7: n in [1..17] ];
%Y Cf. A089823, A091629, A091630, A091631, A091632.
%K base,easy,nonn
%O 1,1
%A _Enoch Haga_, Jan 24 2004
%E Edited and extended by _Ray Chandler_, Feb 07 2004