21313661 has 4 divisors (see below), whose sum is σ = 21323232. Its totient is φ = 21304092.

The previous prime is 21313657. The next prime is 21313673. The reversal of 21313661 is 16631312.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21313661 - 2² = 21313657 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 (21313361) 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, 506 + ... + 6548.

It is an arithmetic number, because the mean of its divisors is an integer number (5330808).

Almost surely, 2^21313661 is an apocalyptic number.

It is an amenable number.

21313661 is a deficient number, since it is larger than the sum of its proper divisors (9571).

21313661 is an equidigital number, since it uses as much as digits as its factorization.

21313661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9570.

The product of its digits is 648, while the sum is 23.

The square root of 21313661 is about 4616.6720697923. The cubic root of 21313661 is about 277.2592333094.

Adding to 21313661 its reverse (16631312), we get a palindrome (37944973).

The spelling of 21313661 in words is "twenty-one million, three hundred thirteen thousand, six hundred sixty-one".