21351663 has 12 divisors (see below), whose sum is σ = 30918160. Its totient is φ = 14198976.

The previous prime is 21351661. The next prime is 21351679. The reversal of 21351663 is 36615312.

It is not a de Polignac number, because 21351663 - 2¹ = 21351661 is a prime.

It is a Duffinian number.

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 (21351661) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1158 + ... + 6636.

Almost surely, 2^21351663 is an apocalyptic number.

21351663 is a deficient number, since it is larger than the sum of its proper divisors (9566497).

21351663 is a wasteful number, since it uses less digits than its factorization.

21351663 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5918 (or 5915 counting only the distinct ones).

The product of its digits is 3240, while the sum is 27.

The square root of 21351663 is about 4620.7859721047. The cubic root of 21351663 is about 277.4239187583.

Adding to 21351663 its reverse (36615312), we get a palindrome (57966975).

The spelling of 21351663 in words is "twenty-one million, three hundred fifty-one thousand, six hundred sixty-three".