21163681 has 8 divisors (see below), whose sum is σ = 26385984. Its totient is φ = 16491120.

The previous prime is 21163643. The next prime is 21163687. The reversal of 21163681 is 18636112.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21163681 - 2⁷ = 21163553 is a prime.

It is a super-2 number, since 2×21163681² = 895802786939522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21163687) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 137350 + ... + 137503.

It is an arithmetic number, because the mean of its divisors is an integer number (3298248).

Almost surely, 2^21163681 is an apocalyptic number.

It is an amenable number.

21163681 is a deficient number, since it is larger than the sum of its proper divisors (5222303).

21163681 is a wasteful number, since it uses less digits than its factorization.

21163681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 274871.

The product of its digits is 1728, while the sum is 28.

The square root of 21163681 is about 4600.4000912964. The cubic root of 21163681 is about 276.6073624925.

Adding to 21163681 its reverse (18636112), we get a palindrome (39799793).

The spelling of 21163681 in words is "twenty-one million, one hundred sixty-three thousand, six hundred eighty-one".