19

This number is a prime.

Just showing those entries submitted by 'Honaker': (Click here to show all)

19 terms are required in the Gregory-Leibniz series, i.e., 4(1 - 1/3 + 1/5 - 1/7 + 1/9 - ...), for the first appearance of "3.1" in the decimal expansion of π. [Honaker]

The third term of the sequence where 2^2*3^3*...*a(n)^a(n) + 1 is prime, a(n) is prime, a(n)>a(n-1), and a(n) is minimal. [Honaker]

Q: How many terms of the series 1 + 1/3 + 1/4 + ... + 1/11 + 1/13 + ... (which excludes all denominators containing 2) is required to produce a sum greater than 19? Update: Chuck Gaydos of Arizona has found that the number of terms required to reach the first n natural numbers correspond to 1, 6, 19, 75, 315, 1320, 7141, 43593, 305341, 2593023, 28084553, 400994353, ... . [Honaker]

The number of primes ending with the digit 1 and primes ending with the digit 9 are tied for the first time at 19. [Honaker]