Number of the day: 839

Properties of the number 839:

839 is a cyclic number.
839 is the 146^th prime.
839 has 9 antidivisors and 838 totatives.
839 has an oblong digit sum 20 in base 10.
Reversing the decimal digits of 839 results in a sphenic number.
839 = 420² - 419² is the difference of 2 nonnegative squares in 1 way.
839 is the sum of 2 positive triangular numbers.
839 is the difference of 2 positive pentagonal numbers in 1 way.
839 is not the sum of 3 positive squares.
839² is the sum of 3 positive squares.
839 is a proper divisor of 2⁴¹⁹ - 1.
839 is an emirp in (at least) the following bases: 2, 7, 11, 12, 21, 25, 26, 27, 29, 31, 33, 35, 36, 37, 42, 44, 49, 53, 57, 61, 64, 65, 67, 71, 74, 75, 76, 77, 79, 83, 85, 89, and 92.
839 is palindromic in (at least) the following bases: 4, -10, -19, and -27.
839 in base 28 = 11r and consists of only the digits '1' and 'r'.

The number 839 belongs to the following On-Line Encyclopedia of Integer Sequences (OEIS) sequences (among others):

Sequence numbers and descriptions below are taken from OEIS.
A000928: Irregular primes: p is regular if and only if the numerators of the Bernoulli numbers B_2, B_4, ..., B_{p-3} (A000367) are not divisible by p.
A005385: Safe primes p: (p-1)/2 is also prime.
A007522: Primes of the form 8n+7, that is, primes congruent to -1 mod 8.
A008865: a(n) = n^2 - 2.
A014616: a(n) = solution to the postage stamp problem with 2 denominations and n stamps.
A028871: Primes of the form n^2 - 2.
A068231: Primes congruent to 11 mod 12.
A107132: Primes of the form 2x^2 + 13y^2.
A141123: Primes of the form -x^2+2*x*y+2*y^2 (as well as of the form 3*x^2+6*x*y+2*y^2).
A235229: Numbers whose sum of digits is 20.