Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #26 Jan 17 2019 13:44:08
%S 4,48,64,313,484,642,11950,15845,18580,50929
%N Numbers n such that 10^n - 51 is prime.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/aaaba.htm">Near-repdigit numbers of the form AA...AABA</a>.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/9/99949.htm#prime">Prime numbers of the form 99...9949</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%e 10^4 - 51 = 9949 which is a prime number.
%p A178429:=n->`if`(isprime(10^n-51), n, NULL): seq(A178429(n), n=1..1000); # _Wesley Ivan Hurt_, Nov 26 2014
%t m = 1000; For[n = 1, n < m, If[PrimeQ[10^n - 51], Print[n]]; n++ ]
%o (PARI) is(n)=ispseudoprime(10^n-51) \\ _Charles R Greathouse IV_, Jun 06 2017
%Y Cf. A108330, A108328.
%K more,nonn
%O 1,1
%A _Robert Price_, Dec 21 2010
%E a(10) = 50929 found by _Robert Price_ and added by _Patrick De Geest_, Nov 26 2014