20905681 has 8 divisors (see below), whose sum is σ = 22131200. Its totient is φ = 19692720.

The previous prime is 20905679. The next prime is 20905711. The reversal of 20905681 is 18650902.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 20905681 - 2¹ = 20905679 is a prime.

It is a super-2 number, since 2×20905681² = 874094996147522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (20903681) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 400 + ... + 6478.

It is an arithmetic number, because the mean of its divisors is an integer number (2766400).

Almost surely, 2^20905681 is an apocalyptic number.

It is an amenable number.

20905681 is a deficient number, since it is larger than the sum of its proper divisors (1225519).

20905681 is a wasteful number, since it uses less digits than its factorization.

20905681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6279.

The product of its (nonzero) digits is 4320, while the sum is 31.

The square root of 20905681 is about 4572.2730670860. The cubic root of 20905681 is about 275.4787517250.

The spelling of 20905681 in words is "twenty million, nine hundred five thousand, six hundred eighty-one".