21201557751 has 24 divisors (see below), whose sum is σ = 33430026240. Its totient is φ = 12841155600.

The previous prime is 21201557749. The next prime is 21201557777. The reversal of 21201557751 is 15775510212.

21201557751 is a `hidden beast` number, since 2 + 1 + 20 + 15 + 577 + 51 = 666.

It is not a de Polignac number, because 21201557751 - 2¹ = 21201557749 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21201550751) 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, 87370 + ... + 223688.

It is an arithmetic number, because the mean of its divisors is an integer number (1392917760).

Almost surely, 2^21201557751 is an apocalyptic number.

21201557751 is a deficient number, since it is larger than the sum of its proper divisors (12228468489).

21201557751 is a wasteful number, since it uses less digits than its factorization.

21201557751 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 137907 (or 137904 counting only the distinct ones).

The product of its (nonzero) digits is 24500, while the sum is 36.

The spelling of 21201557751 in words is "twenty-one billion, two hundred one million, five hundred fifty-seven thousand, seven hundred fifty-one".