21405968640 has 216 divisors, whose sum is σ = 84643086528. Its totient is φ = 4892774400.

The previous prime is 21405968629. The next prime is 21405968657. The reversal of 21405968640 is 4686950412.

21405968640 is a `hidden beast` number, since 2 + 14 + 0 + 596 + 8 + 6 + 40 = 666.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 52086 + ... + 213365.

Almost surely, 2^21405968640 is an apocalyptic number.

21405968640 is a gapful number since it is divisible by the number (20) 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 21405968640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (42321543264).

21405968640 is an abundant number, since it is smaller than the sum of its proper divisors (63237117888).

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

21405968640 is a wasteful number, since it uses less digits than its factorization.

21405968640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 265485 (or 265468 counting only the distinct ones).

The product of its (nonzero) digits is 414720, while the sum is 45.

The spelling of 21405968640 in words is "twenty-one billion, four hundred five million, nine hundred sixty-eight thousand, six hundred forty".