21521975481 has 20 divisors (see below), whose sum is σ = 33019038052. Its totient is φ = 13960198368.

The previous prime is 21521975479. The next prime is 21521975483. The reversal of 21521975481 is 18457912512.

21521975481 is a `hidden beast` number, since 2 + 15 + 2 + 1 + 97 + 548 + 1 = 666.

It is an interprime number because it is at equal distance from previous prime (21521975479) and next prime (21521975483).

It can be written as a sum of positive squares in 2 ways, for example, as 15704099856 + 5817875625 = 125316^2 + 76275^2 .

It is not a de Polignac number, because 21521975481 - 2¹ = 21521975479 is a prime.

It is a super-2 number, since 2×21521975481² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21521975483) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 3587590 + ... + 3593583.

Almost surely, 2^21521975481 is an apocalyptic number.

It is an amenable number.

21521975481 is a deficient number, since it is larger than the sum of its proper divisors (11497062571).

21521975481 is an equidigital number, since it uses as much as digits as its factorization.

21521975481 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7181222 (or 7181213 counting only the distinct ones).

The product of its digits is 201600, while the sum is 45.

The spelling of 21521975481 in words is "twenty-one billion, five hundred twenty-one million, nine hundred seventy-five thousand, four hundred eighty-one".