21321663 has 16 divisors (see below), whose sum is σ = 31104000. Its totient is φ = 12884480.

The previous prime is 21321661. The next prime is 21321683. The reversal of 21321663 is 36612312.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 21321663 - 2¹ = 21321661 is a prime.

It is a super-2 number, since 2×21321663² = 909226626171138, which contains 22 as substring.

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21321661) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 14098 + ... + 15536.

It is an arithmetic number, because the mean of its divisors is an integer number (1944000).

Almost surely, 2^21321663 is an apocalyptic number.

21321663 is a deficient number, since it is larger than the sum of its proper divisors (9782337).

21321663 is a wasteful number, since it uses less digits than its factorization.

21321663 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1902.

The product of its digits is 1296, while the sum is 24.

The square root of 21321663 is about 4617.5386300496. The cubic root of 21321663 is about 277.2939270330.

Adding to 21321663 its reverse (36612312), we get a palindrome (57933975).

The spelling of 21321663 in words is "twenty-one million, three hundred twenty-one thousand, six hundred sixty-three".