Number of the day: 31109

Properties of the number 31109:

31109 = 13 × 2393 is semiprime and squarefree.
31109 has 2 distinct prime factors, 4 divisors, 13 antidivisors and 28704 totatives.
31109 has a semiprime digit sum 14 in base 10.
Reversing the decimal digits of 31109 results in an emirpimes.
31109 = 15555² - 15554² = 1203² - 1190² is the difference of 2 nonnegative squares in 2 ways.
31109 is the difference of 2 positive pentagonal numbers in 2 ways.
31109 = 47² + 170² = 22² + 175² is the sum of 2 positive squares in 2 ways.
31109 = 47² + 72² + 154² is the sum of 3 positive squares.
31109² = 7700² + 30141² = 4485² + 30784² = 15980² + 26691² = 11965² + 28716² is the sum of 2 positive squares in 4 ways.
31109² is the sum of 3 positive squares.
31109 is a proper divisor of 1279⁸ - 1.
31109 = '3' + '1109' is the concatenation of 2 prime numbers.
31109 is an emirpimes in (at least) the following bases: 2, 3, 5, 10, 11, 14, 17, 18, 19, 20, 22, 25, 28, 29, 31, 32, 34, 38, 40, 41, 42, 47, 51, 58, 65, 66, 69, 71, 73, 74, 77, 78, 81, 83, 85, 87, 91, 94, 97, 98, and 99.
31109 is palindromic in (at least) base -81.

The number 31109 belongs to the following On-Line Encyclopedia of Integer Sequences (OEIS) sequences (among others):

Sequence numbers and descriptions below are taken from OEIS.
A009178: Expansion of cosh(x)*cosh(log(1+x)).
A056938: Concatenate all the prime divisors in previous term (with repetition), starting at 49.
A120884: (1/8)*number of lattice points with odd indices in a cubic lattice inside a sphere around the origin with radius 2*n.
A147466: Number of n X n binary arrays symmetric under 180 degree rotation with all ones connected only in a 1100-1111-0011 pattern in any orientation.
A148991: Number of walks within N^3 (the first octant of Z^3) starting at (0,0,0) and consisting of n steps taken from {(-1, -1, 0), (-1, 1, -1), (0, 1, 1), (1, -1, 1), (1, 0, -1)}
A183899: Number of nondecreasing arrangements of n+3 numbers in 0..4 with each number being the sum mod 5 of three others
A186636: a(n) = n*(n^3+n^2+2*n+1).