1991296820 has 12 divisors (see below), whose sum is σ = 4181723364. Its totient is φ = 796518720.

The previous prime is 1991296771. The next prime is 1991296823. The reversal of 1991296820 is 286921991.

It can be written as a sum of positive squares in 2 ways, for example, as 1236366244 + 754930576 = 35162^2 + 27476^2 .

It is a super-2 number, since 2×1991296820² = 7930526050684224800, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991296823) 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, 49782401 + ... + 49782440.

It is an arithmetic number, because the mean of its divisors is an integer number (348476947).

Almost surely, 2^1991296820 is an apocalyptic number.

1991296820 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

1991296820 is an abundant number, since it is smaller than the sum of its proper divisors (2190426544).

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

1991296820 is a wasteful number, since it uses less digits than its factorization.

1991296820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 99564850 (or 99564848 counting only the distinct ones).

The product of its (nonzero) digits is 139968, while the sum is 47.

The square root of 1991296820 is about 44623.9489512078. The cubic root of 1991296820 is about 1258.0908392661.

The spelling of 1991296820 in words is "one billion, nine hundred ninety-one million, two hundred ninety-six thousand, eight hundred twenty".