21636505 has 16 divisors (see below), whose sum is σ = 28465344. Its totient is φ = 15657280.

The previous prime is 21636499. The next prime is 21636521. The reversal of 21636505 is 50563612.

It is not a de Polignac number, because 21636505 - 2⁵ = 21636473 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11619 + ... + 13351.

It is an arithmetic number, because the mean of its divisors is an integer number (1779084).

Almost surely, 2^21636505 is an apocalyptic number.

It is an amenable number.

21636505 is a deficient number, since it is larger than the sum of its proper divisors (6828839).

21636505 is a wasteful number, since it uses less digits than its factorization.

21636505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1976.

The product of its (nonzero) digits is 5400, while the sum is 28.

The square root of 21636505 is about 4651.5056702105. The cubic root of 21636505 is about 278.6521317162.

It can be divided in two parts, 2163 and 6505, that added together give a palindrome (8668).

The spelling of 21636505 in words is "twenty-one million, six hundred thirty-six thousand, five hundred five".