20640420 has 144 divisors (see below), whose sum is σ = 67511808. Its totient is φ = 5287680.

The previous prime is 20640401. The next prime is 20640437. The reversal of 20640420 is 2404602.

20640420 = T₄₇₉ + T₄₈₀ + ... + T₆₁₅.

20640420 is a `hidden beast` number, since 2 + 0 + 640 + 4 + 20 = 666.

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

It is a junction number, because it is equal to n+sod(n) for n = 20640393 and 20640402.

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 47 ways as a sum of consecutive naturals, for example, 150592 + ... + 150728.

It is an arithmetic number, because the mean of its divisors is an integer number (468832).

Almost surely, 2^20640420 is an apocalyptic number.

20640420 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 20640420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33755904).

20640420 is an abundant number, since it is smaller than the sum of its proper divisors (46871388).

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

20640420 is a wasteful number, since it uses less digits than its factorization.

20640420 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 192 (or 178 counting only the distinct ones).

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

The square root of 20640420 is about 4543.1729000777. The cubic root of 20640420 is about 274.3086546103.

The spelling of 20640420 in words is "twenty million, six hundred forty thousand, four hundred twenty".