1978888691 has 16 divisors (see below), whose sum is σ = 2156112000. Its totient is φ = 1805357568.

The previous prime is 1978888687. The next prime is 1978888693. The reversal of 1978888691 is 1968888791.

It is a cyclic number.

It is not a de Polignac number, because 1978888691 - 2² = 1978888687 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1978888693) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 423335 + ... + 427983.

It is an arithmetic number, because the mean of its divisors is an integer number (134757000).

Almost surely, 2^1978888691 is an apocalyptic number.

1978888691 is a deficient number, since it is larger than the sum of its proper divisors (177223309).

1978888691 is a wasteful number, since it uses less digits than its factorization.

1978888691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5038.

The product of its digits is 13934592, while the sum is 65.

The square root of 1978888691 is about 44484.7017636400. The cubic root of 1978888691 is about 1255.4722625946.

It can be divided in two parts, 197 and 8888691, that added together give a palindrome (8888888).

The spelling of 1978888691 in words is "one billion, nine hundred seventy-eight million, eight hundred eighty-eight thousand, six hundred ninety-one".