20918640 has 80 divisors (see below), whose sum is σ = 66388608. Its totient is φ = 5445888.

The previous prime is 20918629. The next prime is 20918699. The reversal of 20918640 is 4681902.

It is a tau number, because it is divible by the number of its divisors (80).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 20918598 and 20918607.

It is a congruent number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 9307 + ... + 11333.

Almost surely, 2^20918640 is an apocalyptic number.

20918640 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 20918640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33194304).

20918640 is an abundant number, since it is smaller than the sum of its proper divisors (45469968).

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

20918640 is a wasteful number, since it uses less digits than its factorization.

20918640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2086 (or 2080 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 30.

The square root of 20918640 is about 4573.6899763757. The cubic root of 20918640 is about 275.5356611644.

It can be divided in two parts, 2091 and 8640, that added together give a triangular number (10731 = T₁₄₆).

The spelling of 20918640 in words is "twenty million, nine hundred eighteen thousand, six hundred forty".