21581002942821 has 24 divisors (see below), whose sum is σ = 35627651701824. Its totient is φ = 12331354697280.

The previous prime is 21581002942789. The next prime is 21581002942847. The reversal of 21581002942821 is 12824920018512.

21581002942821 is a `hidden beast` number, since 2 + 1 + 5 + 81 + 0 + 0 + 294 + 282 + 1 = 666.

It is not a de Polignac number, because 21581002942821 - 2⁵ = 21581002942789 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21581002942621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 7774251 + ... + 10178456.

It is an arithmetic number, because the mean of its divisors is an integer number (1484485487576).

Almost surely, 2^{21581002942821} is an apocalyptic number.

21581002942821 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21581002942821 is a deficient number, since it is larger than the sum of its proper divisors (14046648759003).

21581002942821 is a wasteful number, since it uses less digits than its factorization.

21581002942821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17971801 (or 17971798 counting only the distinct ones).

The product of its (nonzero) digits is 184320, while the sum is 45.

The spelling of 21581002942821 in words is "twenty-one trillion, five hundred eighty-one billion, two million, nine hundred forty-two thousand, eight hundred twenty-one".