21531072 has 56 divisors (see below), whose sum is σ = 57481216. Its totient is φ = 7112448.

The previous prime is 21531071. The next prime is 21531101. The reversal of 21531072 is 27013512.

It is a super-2 number, since 2×21531072² = 927174122938368, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21531071) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 23943 + ... + 24825.

Almost surely, 2^21531072 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 21531072, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28740608).

21531072 is an abundant number, since it is smaller than the sum of its proper divisors (35950144).

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

21531072 is a wasteful number, since it uses less digits than its factorization.

21531072 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1025 (or 1015 counting only the distinct ones).

The product of its (nonzero) digits is 420, while the sum is 21.

The square root of 21531072 is about 4640.1586179785. The cubic root of 21531072 is about 278.1987778351.

Adding to 21531072 its reverse (27013512), we get a palindrome (48544584).

The spelling of 21531072 in words is "twenty-one million, five hundred thirty-one thousand, seventy-two".