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A271822
Numbers k such that (91*10^k + 11)/3 is prime.
0
1, 2, 4, 6, 12, 13, 14, 17, 19, 31, 50, 58, 81, 87, 161, 234, 244, 482, 505, 676, 1111, 1707, 1929, 2695, 3819, 7708, 28958, 44652, 51508, 56892, 158862, 160249, 162410
OFFSET
1,2
COMMENTS
Numbers k such that the digits 30 followed by k-1 occurrences of the digit 3 followed by the digit 7 is prime (see Example section).
a(34) > 3*10^5.
EXAMPLE
4 is in this sequence because (91*10^4+11)/3 = 303337 is prime.
Initial terms and associated primes:
a(1) = 1, 307;
a(2) = 2, 3037;
a(3) = 4, 303337;
a(4) = 6, 30333337;
a(5) = 12, 30333333333337, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(91*10^# + 11)/3] &]
PROG
(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime((91*10^n + 11)/3), print1(n, ", "))); \\ Altug Alkan, Apr 14 2016
(Magma) [n: n in [1..300] |IsPrime((91*10^n + 11) div 3)]; // Vincenzo Librandi, Apr 15 2016
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 14 2016
EXTENSIONS
a(31)-a(33) from Robert Price, Feb 15 2020
STATUS
approved