21263531 has 4 divisors (see below), whose sum is σ = 21302952. Its totient is φ = 21224112.

The previous prime is 21263519. The next prime is 21263533. The reversal of 21263531 is 13536212.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21263531 is a prime.

It is a super-2 number, since 2×21263531² = 904275501175922, 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 = 21263497 and 21263506.

It is not an unprimeable number, because it can be changed into a prime (21263533) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 18890 + ... + 19983.

It is an arithmetic number, because the mean of its divisors is an integer number (5325738).

Almost surely, 2^21263531 is an apocalyptic number.

21263531 is a deficient number, since it is larger than the sum of its proper divisors (39421).

21263531 is an equidigital number, since it uses as much as digits as its factorization.

21263531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 39420.

The product of its digits is 1080, while the sum is 23.

The square root of 21263531 is about 4611.2396381017. The cubic root of 21263531 is about 277.0416902587.

Adding to 21263531 its reverse (13536212), we get a palindrome (34799743).

The spelling of 21263531 in words is "twenty-one million, two hundred sixty-three thousand, five hundred thirty-one".