21951020 has 72 divisors (see below), whose sum is σ = 57781584. Its totient is φ = 6943104.

The previous prime is 21950987. The next prime is 21951043. The reversal of 21951020 is 2015912.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a junction number, because it is equal to n+sod(n) for n = 21950983 and 21951001.

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 23 ways as a sum of consecutive naturals, for example, 11879 + ... + 13601.

It is an arithmetic number, because the mean of its divisors is an integer number (802522).

Almost surely, 2^21951020 is an apocalyptic number.

21951020 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 21951020, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28890792).

21951020 is an abundant number, since it is smaller than the sum of its proper divisors (35830564).

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

21951020 is a wasteful number, since it uses less digits than its factorization.

21951020 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1759 (or 1750 counting only the distinct ones).

The product of its (nonzero) digits is 180, while the sum is 20.

The square root of 21951020 is about 4685.1915649203. The cubic root of 21951020 is about 279.9958332713.

Adding to 21951020 its reverse (2015912), we get a palindrome (23966932).

The spelling of 21951020 in words is "twenty-one million, nine hundred fifty-one thousand, twenty".