20991960 has 320 divisors, whose sum is σ = 83635200. Its totient is φ = 4665600.

The previous prime is 20991947. The next prime is 20991961. The reversal of 20991960 is 6919902.

20991960 is a nontrivial binomial coefficient, being equal to C(6480, 2).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20991961) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 677145 + ... + 677175.

It is an arithmetic number, because the mean of its divisors is an integer number (261360).

Almost surely, 2^20991960 is an apocalyptic number.

20991960 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

20991960 is the 6479-th triangular number and also the 3240-th hexagonal number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20991960, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (41817600).

20991960 is an abundant number, since it is smaller than the sum of its proper divisors (62643240).

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

20991960 is a wasteful number, since it uses less digits than its factorization.

20991960 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 84 (or 71 counting only the distinct ones).

The product of its (nonzero) digits is 8748, while the sum is 36.

The square root of 20991960 is about 4581.6983750570. The cubic root of 20991960 is about 275.8572040162.

The spelling of 20991960 in words is "twenty million, nine hundred ninety-one thousand, nine hundred sixty".