1998021636 has 36 divisors (see below), whose sum is σ = 5439060172. Its totient is φ = 614775744.

The previous prime is 1998021587. The next prime is 1998021637. The reversal of 1998021636 is 6361208991.

It is a happy number.

1998021636 is a `hidden beast` number, since 1 + 9 + 9 + 8 + 0 + 2 + 1 + 636 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 811908036 + 1186113600 = 28494^2 + 34440^2 .

It is a tau number, because it is divible by the number of its divisors (36).

It is a junction number, because it is equal to n+sod(n) for n = 1998021591 and 1998021600.

It is not an unprimeable number, because it can be changed into a prime (1998021637) 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, 2134171 + ... + 2135106.

Almost surely, 2^1998021636 is an apocalyptic number.

It is an amenable number.

1998021636 is an abundant number, since it is smaller than the sum of its proper divisors (3441038536).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1998021636 is a wasteful number, since it uses less digits than its factorization.

1998021636 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4269300 (or 4269295 counting only the distinct ones).

The product of its (nonzero) digits is 139968, while the sum is 45.

The square root of 1998021636 is about 44699.2352954723. The cubic root of 1998021636 is about 1259.5054824328.

It can be divided in two parts, 19980 and 21636, that added together give a triangular number (41616 = T₂₈₈).

The spelling of 1998021636 in words is "one billion, nine hundred ninety-eight million, twenty-one thousand, six hundred thirty-six".