21212138857 has 12 divisors (see below), whose sum is σ = 26573449476. Its totient is φ = 16783230240.

The previous prime is 21212138819. The next prime is 21212138863. The reversal of 21212138857 is 75883121212.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 1949752336 + 19262386521 = 44156^2 + 138789^2 .

It is not a de Polignac number, because 21212138857 - 2⁷ = 21212138729 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21212138657) 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, 16649394 + ... + 16650667.

It is an arithmetic number, because the mean of its divisors is an integer number (2214454123).

Almost surely, 2^21212138857 is an apocalyptic number.

It is an amenable number.

21212138857 is a deficient number, since it is larger than the sum of its proper divisors (5361310619).

21212138857 is a wasteful number, since it uses less digits than its factorization.

21212138857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 33300088 (or 33300081 counting only the distinct ones).

The product of its digits is 53760, while the sum is 40.

The spelling of 21212138857 in words is "twenty-one billion, two hundred twelve million, one hundred thirty-eight thousand, eight hundred fifty-seven".