A101062 - OEIS

%I #16 Jan 17 2019 13:44:06

%S 0,1,3,4,7,9,21,222,253,349,378,400,435,1153,1245,2052,2686,3724,4270,

%T 13095,21426,30265,36790,41758

%N Indices of primes in sequence defined by A(0) = 83, A(n) = 10*A(n-1) - 7 for n > 0.

%C Numbers n such that (740*10^n + 7)/9 is prime.

%C Numbers n such that digit 8 followed by n >= 0 occurrences of digit 2 followed by digit 3 is prime.

%C Numbers corresponding to terms <= 435 are certified primes.

%C a(25) > 10^5. - _Robert Price_, Oct 15 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/8/82223.htm#prime">Prime numbers of the form 822...223</a>.

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

%F a(n) = A103075(n) - 1. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

%e 822223is prime, hence 4 is a term.

%t Select[Range[0, 100000], PrimeQ[(740*10^# + 7)/9] &] (* _Robert Price_, Oct 15 2015 *)

%o (PARI) a=83;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-7)

%o (PARI) for(n=0,1500,if(isprime((740*10^n+7)/9),print1(n,",")))

%Y Cf. A000533, A002275, A103075.

%K nonn,hard,more

%O 1,3

%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 30 2004

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

%E a(20)-a(24) from Kamada data by _Ray Chandler_, Apr 29 2015