A101394 -id:A101394 - cp's OEIS frontend

A101715 Indices of primes in sequence defined by A(0) = 49, A(n) = 10*A(n-1) - 81 for n > 0.

1, 3, 4, 7, 8, 27, 190, 195, 2037, 34413, 39265, 50578, 94285, 108411, 130479, 178090, 185354

Offset: 1

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 14 2004

Numbers n such that 40*10^n + 9 is prime.
Numbers n such that digit 4 followed by n >= 0 occurrences of digit 0 followed by digit 9 is prime.
Numbers corresponding to terms <= 195 are certified primes.
a(18) > 2*10^5. - Robert Price, May 24 2015

			40009 is prime, hence 3 is a term.

Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.

Makoto Kamada, Prime numbers of the form 400...009.

Cf. A000533, A002275, A101394.

Select[Range[0, 1000], PrimeQ[40*10^# + 9] &] (* Robert Price, May 24 2015 *)

a=49;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-81)

for(n=0,1500,if(isprime(40*10^n+9),print1(n,",")))

a(n) = A101394(n+1) - 1.

2037 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(10)-a(11) from Kamada data by Ray Chandler, Apr 30 2015
a(12)-a(17) from Robert Price, May 24 2015

cp's OEIS Frontend

A101715 Indices of primes in sequence defined by A(0) = 49, A(n) = 10*A(n-1) - 81 for n > 0.

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