1661816691990 has 512 divisors, whose sum is σ = 5637839155200. Its totient is φ = 339013693440.

The previous prime is 1661816691967. The next prime is 1661816692009. The reversal of 1661816691990 is 991966181661.

1661816691990 is a `hidden beast` number, since 1 + 6 + 618 + 1 + 6 + 6 + 9 + 1 + 9 + 9 + 0 = 666.

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

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 255 ways as a sum of consecutive naturals, for example, 88418034 + ... + 88436826.

It is an arithmetic number, because the mean of its divisors is an integer number (11011404600).

Almost surely, 2^{1661816691990} is an apocalyptic number.

1661816691990 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is a practical number, because each smaller number is the sum of distinct divisors of 1661816691990, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2818919577600).

1661816691990 is an abundant number, since it is smaller than the sum of its proper divisors (3976022463210).

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

1661816691990 is a wasteful number, since it uses less digits than its factorization.

1661816691990 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18949 (or 18943 counting only the distinct ones).

The product of its (nonzero) digits is 7558272, while the sum is 63.

The spelling of 1661816691990 in words is "one trillion, six hundred sixty-one billion, eight hundred sixteen million, six hundred ninety-one thousand, nine hundred ninety".