21540681 has 16 divisors (see below), whose sum is σ = 32097600. Its totient is φ = 14277024.

The previous prime is 21540679. The next prime is 21540709. The reversal of 21540681 is 18604512.

It is not a de Polignac number, because 21540681 - 2¹ = 21540679 is a prime.

It is a super-2 number, since 2×21540681² = 928001875887522, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21540611) 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, 2605 + ... + 7061.

It is an arithmetic number, because the mean of its divisors is an integer number (2006100).

Almost surely, 2^21540681 is an apocalyptic number.

It is an amenable number.

21540681 is a deficient number, since it is larger than the sum of its proper divisors (10556919).

21540681 is a wasteful number, since it uses less digits than its factorization.

21540681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4645 (or 4639 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 27.

The square root of 21540681 is about 4641.1939196720. The cubic root of 21540681 is about 278.2401570177.

The spelling of 21540681 in words is "twenty-one million, five hundred forty thousand, six hundred eighty-one".