20402640 has 120 divisors (see below), whose sum is σ = 70218720. Its totient is φ = 5306112.

The previous prime is 20402623. The next prime is 20402647. The reversal of 20402640 is 4620402.

20402640 is a `hidden beast` number, since 20 + 4 + 0 + 2 + 640 = 666.

It is a tau number, because it is divible by the number of its divisors (120).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20402647) 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, 30631 + ... + 31289.

It is an arithmetic number, because the mean of its divisors is an integer number (585156).

Almost surely, 2^20402640 is an apocalyptic number.

20402640 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 20402640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35109360).

20402640 is an abundant number, since it is smaller than the sum of its proper divisors (49816080).

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

20402640 is a wasteful number, since it uses less digits than its factorization.

20402640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 721 (or 712 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 18.

The square root of 20402640 is about 4516.9281597121. The cubic root of 20402640 is about 273.2512279005.

The spelling of 20402640 in words is "twenty million, four hundred two thousand, six hundred forty".