21366681 has 16 divisors (see below), whose sum is σ = 32640000. Its totient is φ = 12179088.

The previous prime is 21366679. The next prime is 21366689. The reversal of 21366681 is 18666312.

It is not a de Polignac number, because 21366681 - 2¹ = 21366679 is a prime.

It is a super-2 number, since 2×21366681² = 913070113911522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21366689) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9460 + ... + 11498.

It is an arithmetic number, because the mean of its divisors is an integer number (2040000).

Almost surely, 2^21366681 is an apocalyptic number.

21366681 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21366681 is a deficient number, since it is larger than the sum of its proper divisors (11273319).

21366681 is a wasteful number, since it uses less digits than its factorization.

21366681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2548.

The product of its digits is 10368, while the sum is 33.

The square root of 21366681 is about 4622.4107346708. The cubic root of 21366681 is about 277.4889468855.

The spelling of 21366681 in words is "twenty-one million, three hundred sixty-six thousand, six hundred eighty-one".