21651263 has 4 divisors (see below), whose sum is σ = 21746040. Its totient is φ = 21556488.

The previous prime is 21651221. The next prime is 21651271. The reversal of 21651263 is 36215612.

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

It is a cyclic number.

It is not a de Polignac number, because 21651263 - 2¹⁸ = 21389119 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21651283) 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, 47045 + ... + 47502.

It is an arithmetic number, because the mean of its divisors is an integer number (5436510).

Almost surely, 2^21651263 is an apocalyptic number.

21651263 is a deficient number, since it is larger than the sum of its proper divisors (94777).

21651263 is an equidigital number, since it uses as much as digits as its factorization.

21651263 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 94776.

The product of its digits is 2160, while the sum is 26.

The square root of 21651263 is about 4653.0917678464. The cubic root of 21651263 is about 278.7154724070.

Adding to 21651263 its reverse (36215612), we get a palindrome (57866875).

The spelling of 21651263 in words is "twenty-one million, six hundred fifty-one thousand, two hundred sixty-three".