A102028 - OEIS

%I #16 Jan 17 2019 13:44:07

%S 0,1,7,9,24,49,75,103,4405,8934,25999,31651

%N Indices of primes in sequence defined by A(0) = 19, A(n) = 10*A(n-1) - 11 for n > 0.

%C Numbers n such that (160*10^n + 11)/9 is prime.

%C Numbers n such that digit 1 followed by n >= 0 occurrences of digit 7 followed by digit 9 is prime.

%C Numbers corresponding to terms <= 103 are certified primes.

%C a(13) > 10^5. - _Robert Price_, Feb 07 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/1/17779.htm#prime">Prime numbers of the form 177...779</a>.

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

%F a(n) = A102943(n) - 1.

%e 179 is prime, hence 1 is a term.

%o (PARI) a=19;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-11)

%o (PARI) for(n=0,1500,if(isprime((160*10^n+11)/9),print1(n,",")))

%Y Cf. A000533, A002275, A102943.

%K nonn,hard,more

%O 1,3

%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004

%E More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

%E a(11)-a(12) derived from A102943 by _Robert Price_, Feb 07 2015