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%I #15 Jan 17 2019 13:44:06
%S 0,2,5,11,407,648,948,962,1004,2699,19778,22517,22610,40583,55361,
%T 70193
%N Indices of primes in sequence defined by A(0) = 31, A(n) = 10*A(n-1) + 11 for n > 0.
%C Numbers n such that (290*10^n - 11)/9 is prime.
%C Numbers n such that digit 3 followed by n >= 0 occurrences of digit 2 followed by digit 1 is prime.
%C Numbers corresponding to terms <= 962 are certified primes.
%C a(17) > 10^5. - _Robert Price_, Apr 04 2015
%D Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/3/32221.htm#prime">Prime numbers of the form 322...221</a>.
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = A102966(n+1) - 1.
%e 3221 is prime, hence 2 is a term.
%t Select[Range[0, 1000], PrimeQ[(290*10^# - 11)/9] &](* _Robert Price_, Apr 04 2015 *)
%o (PARI) a=31;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+11)
%o (PARI) for(n=0,1500,if(isprime((290*10^n-11)/9),print1(n,",")))
%Y Cf. A000533, A002275, A102966.
%K nonn,hard,more
%O 1,2
%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004
%E 2699 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
%E a(11)-a(16) derived from A102966 by _Robert Price_, Apr 04 2015
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