21721896 has 144 divisors (see below), whose sum is σ = 70424640. Its totient is φ = 6027840.

The previous prime is 21721879. The next prime is 21721901. The reversal of 21721896 is 69812712.

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

It is a nude number because it is divisible by every one of its digits.

It is a self number, because there is not a number n which added to its sum of digits gives 21721896.

It is an unprimeable number.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 165751 + ... + 165881.

It is an arithmetic number, because the mean of its divisors is an integer number (489060).

Almost surely, 2^21721896 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21721896, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35212320).

21721896 is an abundant number, since it is smaller than the sum of its proper divisors (48702744).

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

21721896 is a wasteful number, since it uses less digits than its factorization.

21721896 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 204 (or 190 counting only the distinct ones).

The product of its digits is 12096, while the sum is 36.

The square root of 21721896 is about 4660.6754875232. The cubic root of 21721896 is about 279.0182282768.

The spelling of 21721896 in words is "twenty-one million, seven hundred twenty-one thousand, eight hundred ninety-six".