20643840 has 204 divisors, whose sum is σ = 81788304. Its totient is φ = 4718592.

The previous prime is 20643809. The next prime is 20643851. The reversal of 20643840 is 4834602.

It is a Jordan-Polya number, since it can be written as 8! ⋅ (2!)⁹.

It is a zygodrome in base 8.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2949117 + ... + 2949123.

Almost surely, 2^20643840 is an apocalyptic number.

20643840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20643840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40894152).

20643840 is an abundant number, since it is smaller than the sum of its proper divisors (61144464).

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

20643840 is an frugal number, since it uses more digits than its factorization.

20643840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 50 (or 17 counting only the distinct ones).

The product of its (nonzero) digits is 4608, while the sum is 27.

The square root of 20643840 is about 4543.5492734205. The cubic root of 20643840 is about 274.3238042340.

The spelling of 20643840 in words is "twenty million, six hundred forty-three thousand, eight hundred forty".