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%I #15 Mar 06 2022 09:01:10
%S 3,3,43,236367611,31542795419
%N Least prime p such that f(0),...,f(n) are all primes, where f(0) = p, then f(i+1) = triangular(f(i))+1.
%C Triangular(p) = p*(p+1)/2 (see A034953).
%e a(2) = 3 because 3 is the least prime such that the following are two primes:
%e p1 = 3 * 4 / 2 + 1 = 7.
%e p2 = 7 * 8 / 2 + 1 = 29.
%e a(3) = 43 because 43 is the least prime such that the following are three primes:
%e p1 = 43 * 44 / 2 + 1 = 947.
%e p2 = 947 * 948 / 2 + 1 = 448879.
%e p3 = 448879 * 448880 / 2 + 1 = 100746402761.
%Y Cf. A000040, A000217, A034953, A231847, A231988.
%K nonn,hard,more
%O 1,1
%A _Alex Ratushnyak_, Nov 16 2013
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