21131520 has 72 divisors (see below), whose sum is σ = 67501056. Its totient is φ = 5634048.

The previous prime is 21131519. The next prime is 21131531. The reversal of 21131520 is 2513112.

It is a super-2 number, since 2×21131520² = 893082275020800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 21131520.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1089 + ... + 6591.

Almost surely, 2^21131520 is an apocalyptic number.

21131520 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 21131520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33750528).

21131520 is an abundant number, since it is smaller than the sum of its proper divisors (46369536).

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

21131520 is an equidigital number, since it uses as much as digits as its factorization.

21131520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5527 (or 5513 counting only the distinct ones).

The product of its (nonzero) digits is 60, while the sum is 15.

The square root of 21131520 is about 4596.9033054873. The cubic root of 21131520 is about 276.4671776890.

Adding to 21131520 its reverse (2513112), we get a palindrome (23644632).

The spelling of 21131520 in words is "twenty-one million, one hundred thirty-one thousand, five hundred twenty".