21153531 has 16 divisors (see below), whose sum is σ = 32313600. Its totient is φ = 12057888.

The previous prime is 21153497. The next prime is 21153533. The reversal of 21153531 is 13535112.

It is not a de Polignac number, because 21153531 - 2⁹ = 21153019 is a prime.

It is a super-2 number, since 2×21153531² = 894943747535922, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a junction number, because it is equal to n+sod(n) for n = 21153498 and 21153507.

It is not an unprimeable number, because it can be changed into a prime (21153533) 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, 9700 + ... + 11678.

It is an arithmetic number, because the mean of its divisors is an integer number (2019600).

Almost surely, 2^21153531 is an apocalyptic number.

21153531 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21153531 is a deficient number, since it is larger than the sum of its proper divisors (11160069).

21153531 is a wasteful number, since it uses less digits than its factorization.

21153531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2498.

The product of its digits is 450, while the sum is 21.

The square root of 21153531 is about 4599.2967940762. The cubic root of 21153531 is about 276.5631355662.

Adding to 21153531 its reverse (13535112), we get a palindrome (34688643).

The spelling of 21153531 in words is "twenty-one million, one hundred fifty-three thousand, five hundred thirty-one".