19919

Properties

Appears in sequences

• Primes that contain digits 1 and 9 only.at n=10A020457
• Numbers k such that sigma(k-1) divides sigma(k+1).at n=32A067130
• Numbers n such that sigma(n+1) = 2*sigma(n-1).at n=4A067134
• Value of C in y = x^2+7x+C such that y is prime for all x = 0 to 4.at n=27A097436
• Primes in which the frequency of every digit is also prime.at n=14A113615
• Primes congruent to 36 mod 59.at n=36A142763
• Primes congruent to 33 mod 61.at n=39A142831
• Primes of the form XYX, where Y is a single digit.at n=27A154270
• Number of ways to place zero or more nonadjacent 0,0 1,0 2,1 3,0 3,1 4,0 5,1 6,1 polyhexes in any orientation on a planar n X n X n triangular grid.at n=7A155414
• Primes having only {0, 1, 9} as digits.at n=30A199329
• Number of -n..n arrays x(0..3) of 4 elements with zero sum and no element more than one greater than the previous.at n=41A199848
• Number of sphenic numbers, i.e., numbers with exactly three distinct prime factors, up to 10^n.at n=4A215218
• Primes of the form abcabc..abcab.at n=12A228627
• Primes p such that (2*p)^3 + 1 is a semiprime.at n=48A237038
• Absolute discriminants of complex quadratic fields with 3-class rank 2.at n=21A242862
• Number of isoscent sequences of length n with maximal number of ascents.at n=20A243237
• Primes having only {1, 4, 9} as digits.at n=37A260271
• Numbers k such that 10^k - 20001 is prime.at n=21A278397
• Numbers using only digits 1 and 9.at n=43A284294
• a(n) = (1/2)*A289787(n).at n=6A289788