20684640 has 48 divisors (see below), whose sum is σ = 65158128. Its totient is φ = 5515776.

The previous prime is 20684639. The next prime is 20684641. The reversal of 20684640 is 4648602.

It is an interprime number because it is at equal distance from previous prime (20684639) and next prime (20684641).

It is a tau number, because it is divible by the number of its divisors (48).

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 = 20684598 and 20684607.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20684641) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 21067 + ... + 22026.

It is an arithmetic number, because the mean of its divisors is an integer number (1357461).

Almost surely, 2^20684640 is an apocalyptic number.

20684640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20684640 is an abundant number, since it is smaller than the sum of its proper divisors (44473488).

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

20684640 is a wasteful number, since it uses less digits than its factorization.

20684640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 43111 (or 43103 counting only the distinct ones).

The product of its (nonzero) digits is 9216, while the sum is 30.

The square root of 20684640 is about 4548.0369391640. The cubic root of 20684640 is about 274.5044076784.

The spelling of 20684640 in words is "twenty million, six hundred eighty-four thousand, six hundred forty".