1661971878 has 32 divisors (see below), whose sum is σ = 4220881920. Its totient is φ = 474849000.

The previous prime is 1661971873. The next prime is 1661971889. The reversal of 1661971878 is 8781791661.

1661971878 is a `hidden beast` number, since 1 + 6 + 619 + 7 + 18 + 7 + 8 = 666.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1661971873) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 2197998 + ... + 2198753.

It is an arithmetic number, because the mean of its divisors is an integer number (131902560).

Almost surely, 2^1661971878 is an apocalyptic number.

1661971878 is a gapful number since it is divisible by the number (18) formed by its first and last digit.

1661971878 is an abundant number, since it is smaller than the sum of its proper divisors (2558910042).

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

1661971878 is a wasteful number, since it uses less digits than its factorization.

1661971878 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4396769 (or 4396763 counting only the distinct ones).

The product of its digits is 1016064, while the sum is 54.

The square root of 1661971878 is about 40767.2893138604. The cubic root of 1661971878 is about 1184.5167970644.

The spelling of 1661971878 in words is "one billion, six hundred sixty-one million, nine hundred seventy-one thousand, eight hundred seventy-eight".