21636991 has 8 divisors (see below), whose sum is σ = 22820480. Its totient is φ = 20458008.

The previous prime is 21636961. The next prime is 21637009. The reversal of 21636991 is 19963612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21636991 - 2¹³ = 21628799 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21636991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21636961) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 14230 + ... + 15676.

It is an arithmetic number, because the mean of its divisors is an integer number (2852560).

Almost surely, 2^21636991 is an apocalyptic number.

21636991 is a deficient number, since it is larger than the sum of its proper divisors (1183489).

21636991 is a wasteful number, since it uses less digits than its factorization.

21636991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2253.

The product of its digits is 17496, while the sum is 37.

The square root of 21636991 is about 4651.5579110659. The cubic root of 21636991 is about 278.6542180655.

The spelling of 21636991 in words is "twenty-one million, six hundred thirty-six thousand, nine hundred ninety-one".