21539691 has 12 divisors (see below), whose sum is σ = 31463640. Its totient is φ = 14197920.

The previous prime is 21539681. The next prime is 21539701. The reversal of 21539691 is 19693512.

It is an interprime number because it is at equal distance from previous prime (21539681) and next prime (21539701).

It is not a de Polignac number, because 21539691 - 2⁵ = 21539659 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21539611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 12645 + ... + 14246.

It is an arithmetic number, because the mean of its divisors is an integer number (2621970).

Almost surely, 2^21539691 is an apocalyptic number.

21539691 is a deficient number, since it is larger than the sum of its proper divisors (9923949).

21539691 is a wasteful number, since it uses less digits than its factorization.

21539691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26986 (or 26983 counting only the distinct ones).

The product of its digits is 14580, while the sum is 36.

The square root of 21539691 is about 4641.0872648551. The cubic root of 21539691 is about 278.2358943550.

The spelling of 21539691 in words is "twenty-one million, five hundred thirty-nine thousand, six hundred ninety-one".