21136661 has 24 divisors (see below), whose sum is σ = 27722304. Its totient is φ = 15724800.

The previous prime is 21136649. The next prime is 21136663. The reversal of 21136661 is 16663112.

It is not a de Polignac number, because 21136661 - 2¹⁰ = 21135637 is a prime.

It is a hoax number, since the sum of its digits (26) coincides with the sum of the digits of its distinct prime factors.

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 21136661.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21136663) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 19586 + ... + 20636.

It is an arithmetic number, because the mean of its divisors is an integer number (1155096).

Almost surely, 2^21136661 is an apocalyptic number.

It is an amenable number.

21136661 is a deficient number, since it is larger than the sum of its proper divisors (6585643).

21136661 is a wasteful number, since it uses less digits than its factorization.

21136661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1101 (or 1088 counting only the distinct ones).

The product of its digits is 1296, while the sum is 26.

The square root of 21136661 is about 4597.4624522665. The cubic root of 21136661 is about 276.4895960560.

Adding to 21136661 its reverse (16663112), we get a palindrome (37799773).

The spelling of 21136661 in words is "twenty-one million, one hundred thirty-six thousand, six hundred sixty-one".