20781440 has 64 divisors (see below), whose sum is σ = 52326000. Its totient is φ = 7870464.

The previous prime is 20781437. The next prime is 20781451. The reversal of 20781440 is 4418702.

It is a tau number, because it is divible by the number of its divisors (64).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 11306 + ... + 13014.

Almost surely, 2^20781440 is an apocalyptic number.

20781440 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 20781440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26163000).

20781440 is an abundant number, since it is smaller than the sum of its proper divisors (31544560).

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

20781440 is a wasteful number, since it uses less digits than its factorization.

20781440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1747 (or 1735 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 26.

The square root of 20781440 is about 4558.6664716779. Note that the first 3 decimals coincide. The cubic root of 20781440 is about 274.9319501043.

The spelling of 20781440 in words is "twenty million, seven hundred eighty-one thousand, four hundred forty".