19910820978 has 32 divisors (see below), whose sum is σ = 44996212800. Its totient is φ = 6524448768.

The previous prime is 19910820967. The next prime is 19910821013. The reversal of 19910820978 is 87902801991.

It is a hoax number, since the sum of its digits (54) coincides with the sum of the digits of its distinct prime factors.

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

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3121551 + ... + 3127922.

It is an arithmetic number, because the mean of its divisors is an integer number (1406131650).

Almost surely, 2^19910820978 is an apocalyptic number.

19910820978 is a gapful number since it is divisible by the number (18) formed by its first and last digit.

19910820978 is an abundant number, since it is smaller than the sum of its proper divisors (25085391822).

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

19910820978 is a wasteful number, since it uses less digits than its factorization.

19910820978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6249543 (or 6249537 counting only the distinct ones).

The product of its (nonzero) digits is 653184, while the sum is 54.

The spelling of 19910820978 in words is "nineteen billion, nine hundred ten million, eight hundred twenty thousand, nine hundred seventy-eight".