20991025 has 24 divisors (see below), whose sum is σ = 29176704. Its totient is φ = 14846400.

The previous prime is 20991023. The next prime is 20991043. The reversal of 20991025 is 52019902.

It is not a de Polignac number, because 20991025 - 2¹ = 20991023 is a prime.

It is a hoax number, since the sum of its digits (28) coincides with the sum of the digits of its distinct prime factors.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20990984 and 20991002.

It is not an unprimeable number, because it can be changed into a prime (20991023) 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, 9144 + ... + 11206.

It is an arithmetic number, because the mean of its divisors is an integer number (1215696).

Almost surely, 2^20991025 is an apocalyptic number.

20991025 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

20991025 is a deficient number, since it is larger than the sum of its proper divisors (8185679).

20991025 is a wasteful number, since it uses less digits than its factorization.

20991025 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2121 (or 2116 counting only the distinct ones).

The product of its (nonzero) digits is 1620, while the sum is 28.

The square root of 20991025 is about 4581.5963375225. The cubic root of 20991025 is about 275.8531083162.

The spelling of 20991025 in words is "twenty million, nine hundred ninety-one thousand, twenty-five".