21531644901 has 24 divisors (see below), whose sum is σ = 33680818080. Its totient is φ = 13176206496.

The previous prime is 21531644891. The next prime is 21531644923. The reversal of 21531644901 is 10944613512.

It is a happy number.

21531644901 is a `hidden beast` number, since 2 + 1 + 5 + 3 + 1 + 644 + 9 + 0 + 1 = 666.

It is not a de Polignac number, because 21531644901 - 2⁷ = 21531644773 is a prime.

It is a super-2 number, since 2×21531644901² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21531644941) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 493111 + ... + 534996.

It is an arithmetic number, because the mean of its divisors is an integer number (1403367420).

Almost surely, 2^21531644901 is an apocalyptic number.

It is an amenable number.

21531644901 is a deficient number, since it is larger than the sum of its proper divisors (12149173179).

21531644901 is a wasteful number, since it uses less digits than its factorization.

21531644901 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1028305 (or 1028302 counting only the distinct ones).

The product of its (nonzero) digits is 25920, while the sum is 36.

The spelling of 21531644901 in words is "twenty-one billion, five hundred thirty-one million, six hundred forty-four thousand, nine hundred one".