A101393
Numbers k such that 3*10^k + R_k + 6 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Original entry on oeis.org
1, 2, 218, 692, 1805, 2207, 2873, 59135
Offset: 1
Julien Peter Benney (jpbenney(AT)ftml.net), Jan 15 2005
n = 1, 2 are members since 37 and 317 are primes.
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Do[ If[ PrimeQ[(28*10^n+53)/9], Print[n]], {n, 0, 10000}]
A101395
Numbers k such that 4*10^k+7 is prime.
Original entry on oeis.org
0, 1, 3, 9, 39, 2323
Offset: 1
Julien Peter Benney (jpbenney(AT)ftml.net), Jan 15 2005
n = 1, 3, 9 are members since 47, 4007 and 4000000007 are primes.
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Do[ If[ PrimeQ[4*10^n + 7], Print[n]], {n, 0, 10000}]
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is(n)=ispseudoprime(4*10^n+7) \\ Charles R Greathouse IV, Jun 12 2017
A101824
Indices of primes in sequence defined by A(0) = 37, A(n) = 10*A(n-1) - 63 for n > 0.
Original entry on oeis.org
0, 1, 4, 7, 23, 28, 83, 109, 128, 175, 592, 1136, 2674, 4991, 26903, 31571, 55076, 81020, 122273
Offset: 1
Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004
307 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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a=37;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a-63)
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for(n=0,1500,if(isprime(30*10^n+7),print1(n,",")))
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
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