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a(n)=largest (n+1)-digit prime formed by appending a digit to a(n-1); a(0)=2.
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%I #13 Sep 28 2016 23:14:24

%S 2,29,293,2939,29399,293999,2939999,29399999

%N a(n)=largest (n+1)-digit prime formed by appending a digit to a(n-1); a(0)=2.

%C There is no prime a(8) since 293999991 to 293999999 are all composite.

%C This is also one of five longest possible sequences of primes where each term is formed by appending a digit to the previous term. Alternatively, one can view 29399999 as a prime where truncating the last digit successively always produces a prime. These are called Right-truncatable primes and the other four with 8 digits are 23399339, 37337999, 5939339 and 73939133. A list of all 83 possible Right-truncatable primes can be found in links for A024770. I have independently verified that this list is complete.

%e a(0)=2, a(1)=29, a(2)=293, a(3)=2939, a(4)=29399, a(5)=293999, a(6)=2939999, a(7)=29399999.

%Y Cf. A024770, A000040.

%K base,fini,full,nonn,uned

%O 0,1

%A Vladislav-Stepan Malakhovsky and _Juri-Stepan Gerasimov_, May 31 2009

%E Syntactically incorrect maple code deleted by R. J. Mathar, Oct 15 2011