1661971879 has 4 divisors (see below), whose sum is σ = 1663366176. Its totient is φ = 1660577584.

The previous prime is 1661971873. The next prime is 1661971889. The reversal of 1661971879 is 9781791661.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 1661971879 - 2¹⁹ = 1661447591 is a prime.

It is a Duffinian number.

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 polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 695359 + ... + 697744.

It is an arithmetic number, because the mean of its divisors is an integer number (415841544).

Almost surely, 2^1661971879 is an apocalyptic number.

1661971879 is a deficient number, since it is larger than the sum of its proper divisors (1394297).

1661971879 is a wasteful number, since it uses less digits than its factorization.

1661971879 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1394296.

The product of its digits is 1143072, while the sum is 55.

The square root of 1661971879 is about 40767.2893261252. The cubic root of 1661971879 is about 1184.5167973020.

The spelling of 1661971879 in words is "one billion, six hundred sixty-one million, nine hundred seventy-one thousand, eight hundred seventy-nine".