1981816668 has 36 divisors (see below), whose sum is σ = 5394946648. Its totient is φ = 609789600.

The previous prime is 1981816649. The next prime is 1981816687. The reversal of 1981816668 is 8666181891.

It is an interprime number because it is at equal distance from previous prime (1981816649) and next prime (1981816687).

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

It is a super-3 number, since 3×1981816668³ (a number of 29 digits) contains 333 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2116858 + ... + 2117793.

Almost surely, 2^1981816668 is an apocalyptic number.

1981816668 is a gapful number since it is divisible by the number (18) formed by its first and last digit.

It is an amenable number.

1981816668 is an abundant number, since it is smaller than the sum of its proper divisors (3413129980).

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

1981816668 is a wasteful number, since it uses less digits than its factorization.

1981816668 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4234674 (or 4234669 counting only the distinct ones).

The product of its digits is 995328, while the sum is 54.

The square root of 1981816668 is about 44517.5995309720. The cubic root of 1981816668 is about 1256.0911591848.

The spelling of 1981816668 in words is "one billion, nine hundred eighty-one million, eight hundred sixteen thousand, six hundred sixty-eight".