A101740 - OEIS

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

%S 0,14,40,63,130,137,191,286,494,965,1090,1365,1713,1773,3252,6330,

%T 35325,36990,59585,88260,127178

%N Indices of primes in sequence defined by A(0) = 47, A(n) = 10*A(n-1) + 27 for n > 0.

%C Numbers n such that (450*10^n - 27)/9 is prime.

%C Numbers n such that digit 4 followed by n >= 0 occurrences of digit 9 followed by digit 7 is prime.

%C Numbers corresponding to terms <= 965 are certified primes.

%C a(22) > 2*10^5. - _Robert Price_, Jul 09 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/4/49997.htm#prime">Prime numbers of the form 499...997</a>.

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

%F a(n) = A103003(n+1) - 1.

%e 4999999999999997 is prime, hence 14 is a term.

%o (PARI) a=47;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+27)

%o (PARI) for(n=0,1500,if(isprime((450*10^n-27)/9),print1(n,",")))

%Y Cf. A000533, A002275, A103003.

%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 01 2008

%E a(17)-a(20) from Kamada data by _Ray Chandler_, May 01 2015

%E a(21) from _Robert Price_, Jul 09 2015