21665415780 has 72 divisors (see below), whose sum is σ = 67838394624. Its totient is φ = 5591073600.

The previous prime is 21665415773. The next prime is 21665415781. The reversal of 21665415780 is 8751456612.

21665415780 is a `hidden beast` number, since 2 + 16 + 65 + 4 + 1 + 578 + 0 = 666.

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

It is not an unprimeable number, because it can be changed into a prime (21665415781) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1935766 + ... + 1946925.

Almost surely, 2^21665415780 is an apocalyptic number.

21665415780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21665415780 is an abundant number, since it is smaller than the sum of its proper divisors (46172978844).

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

21665415780 is a wasteful number, since it uses less digits than its factorization.

21665415780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3882737 (or 3882732 counting only the distinct ones).

The product of its (nonzero) digits is 403200, while the sum is 45.

The spelling of 21665415780 in words is "twenty-one billion, six hundred sixty-five million, four hundred fifteen thousand, seven hundred eighty".