20917840 has 40 divisors (see below), whose sum is σ = 48833928. Its totient is φ = 8332800.

The previous prime is 20917829. The next prime is 20917843. The reversal of 20917840 is 4871902.

It can be written as a sum of positive squares in 4 ways, for example, as 5645376 + 15272464 = 2376^2 + 3908^2 .

It is a tau number, because it is divible by the number of its divisors (40).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20917843) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 29490 + ... + 30190.

It is a vampire number, since it can be written as 2984 ⋅ 7010 (with its own digits).

Almost surely, 2^20917840 is an apocalyptic number.

20917840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20917840 is an abundant number, since it is smaller than the sum of its proper divisors (27916088).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

20917840 is a wasteful number, since it uses less digits than its factorization.

20917840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1087 (or 1081 counting only the distinct ones).

The product of its (nonzero) digits is 4032, while the sum is 31.

The square root of 20917840 is about 4573.6025188029. The cubic root of 20917840 is about 275.5321486458.

The spelling of 20917840 in words is "twenty million, nine hundred seventeen thousand, eight hundred forty".