39973

Appears in sequences

• Numbers k such that 7*10^k + 4*R_k - 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.at n=6A103058
• Apocalypse primes: 10^665+a(n) has 666 decimal digits and is prime.at n=28A115983
• Begin with a(0) = 3. Let a(n) for n > 0 be the smallest positive integer not yet in the sequence which forms part of a Primitive Pythagorean Triple (PPT) when paired with a(n-1).at n=26A239356
• Number of length 3+2 0..n arrays with the sum of second differences multiplied by some arrangement of +-1 equal to zero.at n=11A250562
• Number of (n+2)X(n+2) 0..1 arrays with every 3X3 subblock sum of the two sums of the diagonal and antidiagonal minus the two minimums of the central column and central row nondecreasing horizontally, vertically and ne-to-sw antidiagonally.at n=22A254899