21636440064 has 196 divisors, whose sum is σ = 64893587256. Its totient is φ = 7210156032.

The previous prime is 21636440029. The next prime is 21636440071. The reversal of 21636440064 is 46004463612.

21636440064 is a `hidden beast` number, since 2 + 1 + 6 + 3 + 644 + 0 + 0 + 6 + 4 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 13 ways as a sum of consecutive naturals, for example, 5970157 + ... + 5973779.

Almost surely, 2^21636440064 is an apocalyptic number.

21636440064 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21636440064, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32446793628).

21636440064 is an abundant number, since it is smaller than the sum of its proper divisors (43257147192).

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

21636440064 is an frugal number, since it uses more digits than its factorization.

21636440064 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3667 (or 3628 counting only the distinct ones).

The product of its (nonzero) digits is 82944, while the sum is 36.

The spelling of 21636440064 in words is "twenty-one billion, six hundred thirty-six million, four hundred forty thousand, sixty-four".