1664261891685 has 48 divisors (see below), whose sum is σ = 2923012287936. Its totient is φ = 875888861184.

The previous prime is 1664261891683. The next prime is 1664261891693. The reversal of 1664261891685 is 5861981624661.

1664261891685 is a `hidden beast` number, since 1 + 6 + 6 + 4 + 2 + 618 + 9 + 1 + 6 + 8 + 5 = 666.

It is not a de Polignac number, because 1664261891685 - 2¹ = 1664261891683 is a prime.

It is a super-2 number, since 2×1664261891685² (a number of 25 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1664261891681) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 565002 + ... + 1909908.

It is an arithmetic number, because the mean of its divisors is an integer number (60896089332).

Almost surely, 2^{1664261891685} is an apocalyptic number.

1664261891685 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

It is an amenable number.

1664261891685 is a deficient number, since it is larger than the sum of its proper divisors (1258750396251).

1664261891685 is a wasteful number, since it uses less digits than its factorization.

1664261891685 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1345282 (or 1345279 counting only the distinct ones).

The product of its digits is 29859840, while the sum is 63.

The spelling of 1664261891685 in words is "one trillion, six hundred sixty-four billion, two hundred sixty-one million, eight hundred ninety-one thousand, six hundred eighty-five".