21018743721 has 12 divisors (see below), whose sum is σ = 31339776000. Its totient is φ = 13560479640.

The previous prime is 21018743717. The next prime is 21018743723. The reversal of 21018743721 is 12734781012.

21018743721 is a `hidden beast` number, since 21 + 0 + 187 + 437 + 21 = 666.

It is not a de Polignac number, because 21018743721 - 2² = 21018743717 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21018743723) 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, 37667721 + ... + 37668278.

It is an arithmetic number, because the mean of its divisors is an integer number (2611648000).

Almost surely, 2^21018743721 is an apocalyptic number.

It is an amenable number.

21018743721 is a deficient number, since it is larger than the sum of its proper divisors (10321032279).

21018743721 is a wasteful number, since it uses less digits than its factorization.

21018743721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 75336036 (or 75336033 counting only the distinct ones).

The product of its (nonzero) digits is 18816, while the sum is 36.

The spelling of 21018743721 in words is "twenty-one billion, eighteen million, seven hundred forty-three thousand, seven hundred twenty-one".