20916581 has 24 divisors (see below), whose sum is σ = 25472160. Its totient is φ = 17109792.

The previous prime is 20916559. The next prime is 20916589. The reversal of 20916581 is 18561902.

It is a de Polignac number, because none of the positive numbers 2^k-20916581 is a prime.

It is a super-2 number, since 2×20916581² = 875006721459122, which contains 22 as substring.

It is a Curzon number.

It is a plaindrome in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20916589) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 150410 + ... + 150548.

It is an arithmetic number, because the mean of its divisors is an integer number (1061340).

Almost surely, 2^20916581 is an apocalyptic number.

It is an amenable number.

20916581 is a deficient number, since it is larger than the sum of its proper divisors (4555579).

20916581 is a wasteful number, since it uses less digits than its factorization.

20916581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 273 (or 266 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 32.

The square root of 20916581 is about 4573.4648790605. The cubic root of 20916581 is about 275.5266206382.

It can be divided in two parts, 20916 and 581, that multiplied together give a square (12152196 = 3486²).

The spelling of 20916581 in words is "twenty million, nine hundred sixteen thousand, five hundred eighty-one".