1666561520 has 40 divisors (see below), whose sum is σ = 4172816256. Its totient is φ = 615345408.

The previous prime is 1666561483. The next prime is 1666561553. The reversal of 1666561520 is 251656661.

It is a tau number, because it is divible by the number of its divisors (40).

It is a super-4 number, since 4×1666561520⁴ (a number of 38 digits) contains 4444 as substring.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 800192 + ... + 802271.

Almost surely, 2^1666561520 is an apocalyptic number.

1666561520 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

1666561520 is an abundant number, since it is smaller than the sum of its proper divisors (2506254736).

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

1666561520 is a wasteful number, since it uses less digits than its factorization.

1666561520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1602489 (or 1602483 counting only the distinct ones).

The product of its (nonzero) digits is 64800, while the sum is 38.

The square root of 1666561520 is about 40823.5412476674. The cubic root of 1666561520 is about 1185.6061679407.

The spelling of 1666561520 in words is "one billion, six hundred sixty-six million, five hundred sixty-one thousand, five hundred twenty".