21121891898 has 12 divisors (see below), whose sum is σ = 33120246138. Its totient is φ = 10101773880.

The previous prime is 21121891897. The next prime is 21121891907. The reversal of 21121891898 is 89819812112.

It can be written as a sum of positive squares in only one way, i.e., 16300394929 + 4821496969 = 127673^2 + 69437^2 .

It is a super-2 number, since 2×21121891898² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21121891897) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 9980933 + ... + 9983048.

Almost surely, 2^21121891898 is an apocalyptic number.

21121891898 is a deficient number, since it is larger than the sum of its proper divisors (11998354240).

21121891898 is a wasteful number, since it uses less digits than its factorization.

21121891898 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19964029 (or 19964006 counting only the distinct ones).

The product of its digits is 165888, while the sum is 50.

The spelling of 21121891898 in words is "twenty-one billion, one hundred twenty-one million, eight hundred ninety-one thousand, eight hundred ninety-eight".