A101573 - OEIS

%I #14 Jan 17 2019 13:44:06

%S 1,8,11,14,25,44,61,79,127,325,493,613,709,1640,1645,2102,8513,8687

%N Indices of primes in sequence defined by A(0) = 51, A(n) = 10*A(n-1) + 11 for n > 0.

%C Numbers n such that (470*10^n - 11)/9 is prime.

%C Numbers n such that digit 5 followed by n >= 0 occurrences of digit 2 followed by digit 1 is prime.

%C Numbers corresponding to terms <= 709 are certified primes.

%C a(19) > 10^5. - _Robert Price_, Jul 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/5/52221.htm#prime">Prime numbers of the form 522...221</a>.

%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.

%F a(n) = A103008(n) - 1.

%e 521 is prime, hence 1 is a term.

%o (PARI) a=51;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+11)

%o (PARI) for(n=0,1500,if(isprime((470*10^n-11)/9),print1(n,",")))

%Y Cf. A000533, A002275, A103008.

%K nonn,more

%O 1,2

%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 09 2004

%E More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008