21755172420 has 36 divisors (see below), whose sum is σ = 65990690220. Its totient is φ = 5801379264.

The previous prime is 21755172379. The next prime is 21755172427. The reversal of 21755172420 is 2427155712.

21755172420 is a `hidden beast` number, since 2 + 17 + 55 + 172 + 420 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 16690572864 + 5064599556 = 129192^2 + 71166^2 .

It is a tau number, because it is divible by the number of its divisors (36).

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

It is not an unprimeable number, because it can be changed into a prime (21755172427) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 60430855 + ... + 60431214.

Almost surely, 2^21755172420 is an apocalyptic number.

21755172420 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21755172420 is an abundant number, since it is smaller than the sum of its proper divisors (44235517800).

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

21755172420 is a wasteful number, since it uses less digits than its factorization.

21755172420 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 120862084 (or 120862079 counting only the distinct ones).

The product of its (nonzero) digits is 39200, while the sum is 36.

The spelling of 21755172420 in words is "twenty-one billion, seven hundred fifty-five million, one hundred seventy-two thousand, four hundred twenty".