21651313 has 4 divisors (see below), whose sum is σ = 22397940. Its totient is φ = 20904688.

The previous prime is 21651307. The next prime is 21651323. The reversal of 21651313 is 31315612.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 9345249 + 12306064 = 3057^2 + 3508^2 .

It is a cyclic number.

It is not a de Polignac number, because 21651313 - 2⁵ = 21651281 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21651323) 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, 373270 + ... + 373327.

It is an arithmetic number, because the mean of its divisors is an integer number (5599485).

Almost surely, 2^21651313 is an apocalyptic number.

It is an amenable number.

21651313 is a deficient number, since it is larger than the sum of its proper divisors (746627).

21651313 is an equidigital number, since it uses as much as digits as its factorization.

21651313 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 746626.

The product of its digits is 540, while the sum is 22.

The square root of 21651313 is about 4653.0971406151. The cubic root of 21651313 is about 278.7156869559.

Adding to 21651313 its reverse (31315612), we get a palindrome (52966925).

It can be divided in two parts, 216 and 51313, that added together give a square (51529 = 227²).

The spelling of 21651313 in words is "twenty-one million, six hundred fifty-one thousand, three hundred thirteen".