21636978 has 24 divisors (see below), whose sum is σ = 47567184. Its totient is φ = 6556440.

The previous prime is 21636961. The next prime is 21637009. The reversal of 21636978 is 87963612.

It is a happy number.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 14176 + ... + 15627.

It is an arithmetic number, because the mean of its divisors is an integer number (1981966).

Almost surely, 2^21636978 is an apocalyptic number.

21636978 is an abundant number, since it is smaller than the sum of its proper divisors (25930206).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21636978 is a wasteful number, since it uses less digits than its factorization.

21636978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29830 (or 29819 counting only the distinct ones).

The product of its digits is 108864, while the sum is 42.

The square root of 21636978 is about 4651.5565136844. The cubic root of 21636978 is about 278.6541622582.

The spelling of 21636978 in words is "twenty-one million, six hundred thirty-six thousand, nine hundred seventy-eight".