21617691 has 16 divisors (see below), whose sum is σ = 29774976. Its totient is φ = 13942656.

The previous prime is 21617689. The next prime is 21617699. The reversal of 21617691 is 19671612.

It is not a de Polignac number, because 21617691 - 2¹ = 21617689 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21617699) 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 15 ways as a sum of consecutive naturals, for example, 13836 + ... + 15318.

It is an arithmetic number, because the mean of its divisors is an integer number (1860936).

Almost surely, 2^21617691 is an apocalyptic number.

21617691 is a deficient number, since it is larger than the sum of its proper divisors (8157285).

21617691 is a wasteful number, since it uses less digits than its factorization.

21617691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1642.

The product of its digits is 4536, while the sum is 33.

The square root of 21617691 is about 4649.4828744711. The cubic root of 21617691 is about 278.5713410726.

The spelling of 21617691 in words is "twenty-one million, six hundred seventeen thousand, six hundred ninety-one".