21447972 has 72 divisors (see below), whose sum is σ = 66737216. Its totient is φ = 5655744.

The previous prime is 21447971. The next prime is 21447991. The reversal of 21447972 is 27974412.

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 not an unprimeable number, because it can be changed into a prime (21447971) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 3 + ... + 6549.

Almost surely, 2^21447972 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 21447972, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33368608).

21447972 is an abundant number, since it is smaller than the sum of its proper divisors (45289244).

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

21447972 is a wasteful number, since it uses less digits than its factorization.

21447972 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6577 (or 6572 counting only the distinct ones).

The product of its digits is 28224, while the sum is 36.

The square root of 21447972 is about 4631.1955259954. The cubic root of 21447972 is about 277.8404101020.

The spelling of 21447972 in words is "twenty-one million, four hundred forty-seven thousand, nine hundred seventy-two".