A103001 -id:A103001 - cp's OEIS frontend

A101738 Indices of primes in sequence defined by A(0) = 41, A(n) = 10*A(n-1) + 81 for n > 0.

0, 1, 3, 6, 23, 171, 172, 217, 438, 2562, 2781, 2879, 3714, 4391, 10819, 14591, 25053, 27768, 40167, 180991, 193906

Offset: 1

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

Numbers n such that (450*10^n - 81)/9 is prime.
Numbers n such that digit 4 followed by n >= 0 occurrences of digit 9 followed by digit 1 is prime.
Numbers corresponding to terms <= 438 are certified primes.
a(22) > 2*10^5. - Robert Price, May 30 2015

			49991 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 499...991.
Index entries for primes involving repunits.

Cf. A000533, A002275, A103001.

Select[Range[0, 1000], PrimeQ[(450*10^# - 81)/9] &] (* Robert Price, May 30 2015 *)

a=41;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+81)

for(n=0,1500,if(isprime((450*10^n-81)/9),print1(n,",")))

a(n) = A103001(n) - 1.

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(17)-a(19) from Kamada data by Ray Chandler, May 01 2015
a(20)-a(21) from Robert Price, May 30 2015

A177504 Primes of the form 5*10^n-9.

Original entry on oeis.org

41, 491, 49991, 49999991, 4999999999999999999999991

Offset: 1

Vincenzo Librandi, Dec 11 2010

nonn

Vincenzo Librandi, Table of n, a(n) for n = 1..9

Cf. A086949, A103001.

[a: n in [0..250] | IsPrime(a) where a is 5*10^n-9];

Select[Table[5 10^n - 9, {n, 250}], PrimeQ] (* Vincenzo Librandi, Jan 03 2014 *)

cp's OEIS Frontend

A101738 Indices of primes in sequence defined by A(0) = 41, A(n) = 10*A(n-1) + 81 for n > 0.

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