A101831 - OEIS

%I #20 Sep 08 2022 08:45:16

%S 2,4,8,11,26,50,52,146,154,256,518,602,2884,9508,10523,19649,32507,

%T 79444

%N Indices of primes in sequence defined by A(0) = 39, A(n) = 10*A(n-1) - 61 for n > 0.

%C Numbers n such that (290*10^n + 61)/9 is prime.

%C Numbers n such that digit 3 followed by n >= 0 occurrences of digit 2 followed by digit 9 is prime.

%C a(19) > 10^5. - _Robert Price_, Apr 05 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/3/32229.htm#prime">Prime numbers of the form 322...229</a>.

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

%F a(n) = A102968(n) - 1.

%e 3229 is prime, hence 2 is a term.

%t Select[Range[0, 1000], PrimeQ[(290*10^# + 61)/9] &] (* _Robert Price_, Apr 05 2015 *)

%o (PARI) a=39;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-61)

%o (PARI) for(n=0,1500,if(isprime((290*10^n+61)/9),print1(n,",")))

%o (Magma) [n: n in [0..500] | IsPrime((290*10^n+61) div 9)]; // _Vincenzo Librandi_, Apr 06 2015

%Y Cf. A000533, A002275, A102968.

%K nonn,hard,more

%O 1,1

%A _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004

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

%E a(15)-a(18) derived from A102968 by _Robert Price_, Apr 05 2015