21549681 has 12 divisors (see below), whose sum is σ = 32131840. Its totient is φ = 13902840.

The previous prime is 21549677. The next prime is 21549701. The reversal of 21549681 is 18694512.

It is not a de Polignac number, because 21549681 - 2² = 21549677 is a prime.

It is a super-2 number, since 2×21549681² = 928777502403522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21549611) 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 11 ways as a sum of consecutive naturals, for example, 38341 + ... + 38898.

Almost surely, 2^21549681 is an apocalyptic number.

It is an amenable number.

21549681 is a deficient number, since it is larger than the sum of its proper divisors (10582159).

21549681 is a wasteful number, since it uses less digits than its factorization.

21549681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 77276 (or 77273 counting only the distinct ones).

The product of its digits is 17280, while the sum is 36.

The square root of 21549681 is about 4642.1633965211. The cubic root of 21549681 is about 278.2789025080.

The spelling of 21549681 in words is "twenty-one million, five hundred forty-nine thousand, six hundred eighty-one".