21531066857 has 2 divisors, whose sum is σ = 21531066858. Its totient is φ = 21531066856.

The previous prime is 21531066847. The next prime is 21531066871. The reversal of 21531066857 is 75866013512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21184511401 + 346555456 = 145549^2 + 18616^2 .

It is a cyclic number.

It is not a de Polignac number, because 21531066857 - 2⁴ = 21531066841 is a prime.

It is not a weakly prime, because it can be changed into another prime (21531066827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10765533428 + 10765533429.

It is an arithmetic number, because the mean of its divisors is an integer number (10765533429).

Almost surely, 2^21531066857 is an apocalyptic number.

It is an amenable number.

21531066857 is a deficient number, since it is larger than the sum of its proper divisors (1).

21531066857 is an equidigital number, since it uses as much as digits as its factorization.

21531066857 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 302400, while the sum is 44.

The spelling of 21531066857 in words is "twenty-one billion, five hundred thirty-one million, sixty-six thousand, eight hundred fifty-seven".