21691539 has 12 divisors (see below), whose sum is σ = 31846672. Its totient is φ = 14223600.

The previous prime is 21691531. The next prime is 21691543. The reversal of 21691539 is 93519612.

It is not a de Polignac number, because 21691539 - 2³ = 21691531 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21691531) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 19207 + ... + 20304.

Almost surely, 2^21691539 is an apocalyptic number.

21691539 is a deficient number, since it is larger than the sum of its proper divisors (10155133).

21691539 is a wasteful number, since it uses less digits than its factorization.

21691539 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 39578 (or 39575 counting only the distinct ones).

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

The square root of 21691539 is about 4657.4176321219. The cubic root of 21691539 is about 278.8881889041. Note that the first 3 decimals are identical.

The spelling of 21691539 in words is "twenty-one million, six hundred ninety-one thousand, five hundred thirty-nine".