1661981819904 has 132 divisors (see below), whose sum is σ = 5484498998784. Its totient is φ = 474851930112.

The previous prime is 1661981819903. The next prime is 1661981819929. The reversal of 1661981819904 is 4099181891661.

1661981819904 is a `hidden beast` number, since 1 + 6 + 619 + 8 + 1 + 8 + 1 + 9 + 9 + 0 + 4 = 666.

It is a Harshad number since it is a multiple of its sum of digits (63).

It is not an unprimeable number, because it can be changed into a prime (1661981819903) 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, 12816672 + ... + 12945695.

Almost surely, 2^{1661981819904} is an apocalyptic number.

1661981819904 is a gapful number since it is divisible by the number (14) formed by its first and last digit.

It is an amenable number.

1661981819904 is an abundant number, since it is smaller than the sum of its proper divisors (3822517178880).

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

1661981819904 is a wasteful number, since it uses less digits than its factorization.

1661981819904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25762400 (or 25762379 counting only the distinct ones).

The product of its (nonzero) digits is 6718464, while the sum is 63.

The spelling of 1661981819904 in words is "one trillion, six hundred sixty-one billion, nine hundred eighty-one million, eight hundred nineteen thousand, nine hundred four".