21087128866 has 4 divisors (see below), whose sum is σ = 31630693302. Its totient is φ = 10543564432.

The previous prime is 21087128833. The next prime is 21087128873. The reversal of 21087128866 is 66882178012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 16099803225 + 4987325641 = 126885^2 + 70621^2 .

It is a super-2 number, since 2×21087128866² (a number of 21 digits) contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5271782215 + ... + 5271782218.

Almost surely, 2^21087128866 is an apocalyptic number.

21087128866 is a deficient number, since it is larger than the sum of its proper divisors (10543564436).

21087128866 is a wasteful number, since it uses less digits than its factorization.

21087128866 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10543564435.

The product of its (nonzero) digits is 516096, while the sum is 49.

The spelling of 21087128866 in words is "twenty-one billion, eighty-seven million, one hundred twenty-eight thousand, eight hundred sixty-six".