21531020 has 48 divisors (see below), whose sum is σ = 52170048. Its totient is φ = 7311360.

The previous prime is 21531011. The next prime is 21531023. The reversal of 21531020 is 2013512.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (14).

It is a junction number, because it is equal to n+sod(n) for n = 21530986 and 21531004.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21531023) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 15140 + ... + 16500.

It is an arithmetic number, because the mean of its divisors is an integer number (1086876).

Almost surely, 2^21531020 is an apocalyptic number.

21531020 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 21531020, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26085024).

21531020 is an abundant number, since it is smaller than the sum of its proper divisors (30639028).

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

21531020 is a wasteful number, since it uses less digits than its factorization.

21531020 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1490 (or 1488 counting only the distinct ones).

The product of its (nonzero) digits is 60, while the sum is 14.

The square root of 21531020 is about 4640.1530147184. The cubic root of 21531020 is about 278.1985538743.

Adding to 21531020 its reverse (2013512), we get a palindrome (23544532).

The spelling of 21531020 in words is "twenty-one million, five hundred thirty-one thousand, twenty".