21635871818 has 12 divisors (see below), whose sum is σ = 35672367570. Its totient is φ = 9834487080.

The previous prime is 21635871809. The next prime is 21635871821. The reversal of 21635871818 is 81817853612.

It can be written as a sum of positive squares in only one way, i.e., 18734218129 + 2901653689 = 136873^2 + 53867^2 .

It is a super-2 number, since 2×21635871818² (a number of 21 digits) contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 44701973 + ... + 44702456.

Almost surely, 2^21635871818 is an apocalyptic number.

21635871818 is a deficient number, since it is larger than the sum of its proper divisors (14036495752).

21635871818 is a wasteful number, since it uses less digits than its factorization.

21635871818 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 89404453 (or 89404442 counting only the distinct ones).

The product of its digits is 645120, while the sum is 50.

The spelling of 21635871818 in words is "twenty-one billion, six hundred thirty-five million, eight hundred seventy-one thousand, eight hundred eighteen".