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%I A254928 #32 Dec 10 2016 19:37:07
%S A254928 13,13,13,137,157163,153391501,153391501,1126903901803
%N A254928 Smallest (nontrivial) prime that, for each k from 2 to n, remains prime when each digit is replaced by the digit's k-th power.
%C A254928 Examples of trivial primes are 11, 101, etc, i.e., all primes in the sequence A020449: these generate themselves for all powers. These primes are excluded, otherwise all terms would be 11 since sequence wants smallest primes.
%e A254928 a(5) = 137; (1^k)&(3^k)&(7^k), where "&" represents concatenation of numbers:
%e A254928 for k=2, 1949 (prime), for k=3, 127343 (prime),
%e A254928 for k=4, 1812401 (prime), for k=5, 124316807 (prime).
%Y A254928 Cf. A020449 (primes that contain digits 0 and 1 only).
%Y A254928 Cf. A068492 (primes that remain prime after each digit is replaced by its square).
%Y A254928 Cf. A048393 (replacing digits d in decimal expansion of n with d^3 yields a prime).
%K A254928 nonn,base,hard,more
%O A254928 2,1
%A A254928 _Abhiram R Devesh_, May 04 2015
%E A254928 a(9) from _Giovanni Resta_, May 19 2015

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