21351531 has 4 divisors (see below), whose sum is σ = 28468712. Its totient is φ = 14234352.

The previous prime is 21351509. The next prime is 21351563. The reversal of 21351531 is 13515312.

21351531 is an esthetic number in base 13, because in such base its adjacent digits differ by 1.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 21351531 - 2¹⁵ = 21318763 is a prime.

It is a super-2 number, since 2×21351531² = 911775752087922, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21351498 and 21351507.

It is not an unprimeable number, because it can be changed into a prime (21351571) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3558586 + ... + 3558591.

It is an arithmetic number, because the mean of its divisors is an integer number (7117178).

Almost surely, 2^21351531 is an apocalyptic number.

21351531 is a deficient number, since it is larger than the sum of its proper divisors (7117181).

21351531 is an equidigital number, since it uses as much as digits as its factorization.

21351531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7117180.

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

The square root of 21351531 is about 4620.7716887983. The cubic root of 21351531 is about 277.4233470615.

Adding to 21351531 its reverse (13515312), we get a palindrome (34866843).

The spelling of 21351531 in words is "twenty-one million, three hundred fifty-one thousand, five hundred thirty-one".