

A285570


Numbers k such that (47*10^k + 403)/9 is prime.


0



1, 4, 10, 12, 16, 28, 42, 108, 127, 664, 744, 781, 3036, 3184, 4753, 5695, 7350, 8592, 8694, 15939, 21822, 24466, 61821, 196281
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OFFSET

1,2


COMMENTS

For k > 1, numbers k such that the digit 5 followed by k2 occurrences of the digit 2 followed by the digits 67 is prime (see Example section).
a(25) > 2*10^5.


LINKS



EXAMPLE

4 is in this sequence because (47*10^4 + 403)/9 = 52267 is prime.
Initial terms and associated primes:
a(1) = 1, 97;
a(2) = 4, 52267;
a(3) = 10, 52222222267;
a(4) = 12, 5222222222267;
a(5) = 16, 52222222222222267; etc.


MATHEMATICA

Select[Range[0, 100000], PrimeQ[(47*10^# + 403)/9] &]


CROSSREFS



KEYWORD

nonn,more,hard


AUTHOR



EXTENSIONS



STATUS

approved



