A068651
Primes in which a string of 2's is sandwiched between two 9's.
Original entry on oeis.org
929, 9222229, 9222222222229
Offset: 1
A082703
Numbers k such that (18*10^(k-1) - 81)/9 is a plateau prime.
Original entry on oeis.org
3, 5, 9, 41, 87, 201, 731, 1461, 23673, 28631
Offset: 1
k=9 -> (18*10^(9-1) - 81)/9 = 199999991.
- C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
A056250
Indices of primes in sequence defined by A(0) = 11, A(n) = 10*A(n-1) + 81 for n > 0.
Original entry on oeis.org
0, 1, 3, 7, 39, 85, 199, 729, 1459, 23671, 28629
Offset: 1
191 is prime, hence 1 is a term.
- Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
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Select[Range[0, 2000], PrimeQ[(180 10^# - 81) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *)
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a=11;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+81)
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for(n=0,1500,if(isprime((180*10^n-81)/9),print1(n,",")))
Additional comments from
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 28 2004
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
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