1991561985 has 240 divisors, whose sum is σ = 4567736448. Its totient is φ = 809948160.

The previous prime is 1991561981. The next prime is 1991561993. The reversal of 1991561985 is 5891651991.

1991561985 is a `hidden beast` number, since 1 + 9 + 9 + 15 + 619 + 8 + 5 = 666.

It is not a de Polignac number, because 1991561985 - 2² = 1991561981 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1991561981) by changing a digit.

It is a polite number, since it can be written in 239 ways as a sum of consecutive naturals, for example, 46315374 + ... + 46315416.

Almost surely, 2^1991561985 is an apocalyptic number.

1991561985 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

It is an amenable number.

1991561985 is an abundant number, since it is smaller than the sum of its proper divisors (2576174463).

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

1991561985 is a wasteful number, since it uses less digits than its factorization.

1991561985 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 146 (or 106 counting only the distinct ones).

The product of its digits is 874800, while the sum is 54.

The square root of 1991561985 is about 44626.9199586976. The cubic root of 1991561985 is about 1258.1466800709.

The spelling of 1991561985 in words is "one billion, nine hundred ninety-one million, five hundred sixty-one thousand, nine hundred eighty-five".