21240631521 has 24 divisors (see below), whose sum is σ = 32558128200. Its totient is φ = 13297729536.

The previous prime is 21240631519. The next prime is 21240631523. The reversal of 21240631521 is 12513604212.

21240631521 is a `hidden beast` number, since 2 + 1 + 2 + 4 + 0 + 631 + 5 + 21 = 666.

It is an interprime number because it is at equal distance from previous prime (21240631519) and next prime (21240631523).

It can be written as a sum of positive squares in 4 ways, for example, as 12374337600 + 8866293921 = 111240^2 + 94161^2 .

It is not a de Polignac number, because 21240631521 - 2¹ = 21240631519 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21240631523) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 85900 + ... + 223293.

It is an arithmetic number, because the mean of its divisors is an integer number (1356588675).

Almost surely, 2^21240631521 is an apocalyptic number.

It is an amenable number.

21240631521 is a deficient number, since it is larger than the sum of its proper divisors (11317496679).

21240631521 is a wasteful number, since it uses less digits than its factorization.

21240631521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 309665 (or 309662 counting only the distinct ones).

The product of its (nonzero) digits is 2880, while the sum is 27.

The spelling of 21240631521 in words is "twenty-one billion, two hundred forty million, six hundred thirty-one thousand, five hundred twenty-one".