Number of the day: 2581

Properties of the number 2581:

2581 is a cyclic number.
2581 = 29 × 89 is semiprime and squarefree.
2581 has 2 distinct prime factors, 4 divisors, 7 antidivisors and 2464 totatives.
2581 = 1291² - 1290² = 59² - 30² is the difference of 2 nonnegative squares in 2 ways.
2581 is the difference of 2 positive pentagonal numbers in 1 way.
2581 = 30² + 41² = 9² + 50² is the sum of 2 positive squares in 2 ways.
2581 = 9² + 14² + 48² is the sum of 3 positive squares.
2581² = 1780² + 1869² = 781² + 2460² = 900² + 2419² = 1131² + 2320² is the sum of 2 positive squares in 4 ways.
2581² is the sum of 3 positive squares.
2581 is a proper divisor of 233⁴ - 1.
2581 is an emirpimes in (at least) the following bases: 3, 4, 15, 16, 17, 20, 25, 31, 33, 36, 37, 38, 41, 42, 44, 46, 48, 49, 51, 52, 54, 56, 58, 63, 65, 66, 69, 70, 72, 75, 77, 78, 83, 91, 93, 94, and 96.
2581 is palindromic in (at least) the following bases: 18, 43, 88, -23, -60, and -86.
2581 in base 18 = 7h7 and consists of only the digits '7' and 'h'.
2581 in base 22 = 577 and consists of only the digits '5' and '7'.
2581 in base 42 = 1JJ and consists of only the digits '1' and 'J'.
2581 in base 43 = 1H1 and consists of only the digits '1' and 'H'.
2581 in base 50 = 11V and consists of only the digits '1' and 'V'.

The number 2581 belongs to the following On-Line Encyclopedia of Integer Sequences (OEIS) sequences (among others):

Sequence numbers and descriptions below are taken from OEIS.
A006327: a(n) = Fibonacci(n) - 3. Number of total preorders.
A017981: Powers of cube root of 2 rounded up.
A017987: Powers of cube root of 4 rounded up.
A045944: Rhombic matchstick numbers: a(n) = n*(3*n+2).
A151725: Number of ON states after n generations of cellular automaton based on square grid with each cell adjacent to its eight neighbors.
A214119: Irregular array T(n,k) of the numbers of non-extendable (complete) non-self-adjacent simple paths ending at each of a minimal subset of nodes within a square lattice bounded by rectangles with nodal dimensions n and 2, n >= 2.
A252167: T(n,k)=Number of (n+2)X(k+2) 0..3 arrays with every 3X3 subblock row and column sum equal to 2 3 4 6 or 7 and every 3X3 diagonal and antidiagonal sum not equal to 2 3 4 6 or 7
A256075: Non-palindromic balanced numbers (in base 10).
A326512: Number of set partitions of {1..n} where every block has the same average.
A326977: Number of integer partitions of n such that the dual of the multiset partition obtained by factoring each part into prime numbers is a (strict) antichain, also called T_1 integer partitions.