21128991669 has 12 divisors (see below), whose sum is σ = 31650012576. Its totient is φ = 14085994284.

The previous prime is 21128991661. The next prime is 21128991679. The reversal of 21128991669 is 96619982112.

21128991669 is a `hidden beast` number, since 211 + 289 + 91 + 6 + 69 = 666.

It is not a de Polignac number, because 21128991669 - 2³ = 21128991661 is a prime.

It is a super-2 number, since 2×21128991669² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21128991661) 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, 43475049 + ... + 43475534.

It is an arithmetic number, because the mean of its divisors is an integer number (2637501048).

Almost surely, 2^21128991669 is an apocalyptic number.

It is an amenable number.

21128991669 is a deficient number, since it is larger than the sum of its proper divisors (10521020907).

21128991669 is an frugal number, since it uses more digits than its factorization.

21128991669 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 86950598 (or 86950586 counting only the distinct ones).

The product of its digits is 839808, while the sum is 54.

The spelling of 21128991669 in words is "twenty-one billion, one hundred twenty-eight million, nine hundred ninety-one thousand, six hundred sixty-nine".