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
A068649
Primes in which a string of 9's is sandwiched between two 1's.
Original entry on oeis.org
11, 191, 19991, 199999991, 19999999999999999999999999999999999999991, 199999999999999999999999999999999999999999999999999999999999999999999999999999999999991
Offset: 1
11 is also a member in which a string of 0 9's is there between two one's.
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a := 1:b := 9:i := 1:for n from 0 to 500 do c := a+10*(10^n-1)/9*b+10^(n+1)*a; if(isprime(c)) then d[i] := c; i := i+1; end if; end do:q := seq(d[j],j=1..i-1);
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Select[Table[FromDigits[Join[{1}, Table[9, {i}], {1}]], {i, 0, 200}], PrimeQ]
A056246
Indices of primes in sequence defined by A(0) = 11, A(n) = 10*A(n-1) + 41 for n > 0.
Original entry on oeis.org
0, 1, 3, 19, 31, 399, 561, 7015, 37683
Offset: 1
151 is a 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[(140 10^# - 41) / 9] &] (* Vincenzo Librandi, Nov 03 2014 *)
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a=11;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+41)
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for(n=0,1500,if(isprime((140*10^n-41)/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
A082699
Numbers k such that (14*10^(k-1) - 41)/9 is a plateau prime.
Original entry on oeis.org
3, 5, 21, 33, 401, 563, 7017, 37685
Offset: 1
k=21 -> (14*10^(21-1) - 41)/9 = 155555555555555555551.
- C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
37685 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
Showing 1-4 of 4 results.
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