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A101712 Indices of primes in sequence defined by A(0) = 41, A(n) = 10*A(n-1) - 9 for n > 0.

%I A101712 #19 Jan 17 2019 13:44:06
%S A101712 0,1,2,12,228,241,308,956,1472,1493,3181,3726,4176,23209,25718,32834,
%T A101712 36989,103957
%N A101712 Indices of primes in sequence defined by A(0) = 41, A(n) = 10*A(n-1) - 9 for n > 0.
%C A101712 Numbers n such that 40*10^n + 1 is prime.
%C A101712 Numbers n such that digit 4 followed by n >= 0 occurrences of digit 0 followed by digit 1 is prime.
%D A101712 Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
%H A101712 Makoto Kamada, <a href="https://stdkmd.net/nrr/4/40001.htm#prime">Prime numbers of the form 400...001</a>.
%F A101712 a(n) = A056806(n+1) - 1.
%e A101712 4001 is prime, hence 2 is a term.
%t A101712 Select[Range[0, 1500], PrimeQ[4*10^# + 1] &] (* _Robert Price_, Mar 19 2015 *)
%o A101712 (PARI) a=41;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-9)
%o A101712 (PARI) for(n=0,1500,if(isprime(40*10^n+1),print1(n,",")))
%Y A101712 Cf. A000533, A002275, A056806.
%K A101712 nonn,hard,more
%O A101712 1,3
%A A101712 _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004
%E A101712 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
%E A101712 Added missing term a(16)=32834 by _Robert Price_, Mar 19 2015