A101724 - OEIS

%I #15 Jan 17 2019 13:44:06

%S 0,2,4,5,7,14,25,52,59,96,182,204,301,395,455,466,606,827,1859,2742,

%T 4272,4780,5711,6037,6636,9221,10831,18864,25847,42246,48546,87564,

%U 95587

%N Indices of primes in sequence defined by A(0) = 47, A(n) = 10*A(n-1) - 33 for n > 0.

%C Numbers n such that (390*10^n + 33)/9 is prime.

%C Numbers n such that digit 4 followed by n >= 0 occurrences of digit 3 followed by digit 7 is prime.

%C Numbers corresponding to terms <= 827 are certified primes.

%C a(34) > 10^5. - Robert Price, May 11 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/4/43337.htm#prime">Prime numbers of the form 433...337</a>.

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

%F a(n) = A102989(n) - 1.

%e 4337 is prime, hence 2 is a term.

%t Select[Range[0, 300], PrimeQ[(390*10^# + 33)/9] &] (* _Robert Price_, May 11 2015 *)

%o (PARI) a=47;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-33)

%o (PARI) for(n=0,1500,if(isprime((390*10^n+33)/9),print1(n,",")))

%Y Cf. A000533, A002275, A102989.

%K nonn,hard,more

%O 1,2

%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004

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

%E a(27)-a(31) from Kamada data by _Ray Chandler_, Apr 30 2015

%E a(32)-a(33) from _Robert Price_, May 11 2015