20781990 has 96 divisors (see below), whose sum is σ = 58631040. Its totient is φ = 5104896.

The previous prime is 20781931. The next prime is 20782031. The reversal of 20781990 is 9918702.

It is a happy number.

It is a super-2 number, since 2×20781990² = 863782216720200, which contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 442147 + ... + 442193.

It is an arithmetic number, because the mean of its divisors is an integer number (610740).

Almost surely, 2^20781990 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20781990, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29315520).

20781990 is an abundant number, since it is smaller than the sum of its proper divisors (37849050).

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

20781990 is a wasteful number, since it uses less digits than its factorization.

20781990 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 111 (or 74 counting only the distinct ones).

The product of its (nonzero) digits is 9072, while the sum is 36.

The square root of 20781990 is about 4558.7267959377. The cubic root of 20781990 is about 274.9343755256.

The spelling of 20781990 in words is "twenty million, seven hundred eighty-one thousand, nine hundred ninety".