1991739897 has 72 divisors (see below), whose sum is σ = 3422050632. Its totient is φ = 1112832000.

The previous prime is 1991739881. The next prime is 1991739899. The reversal of 1991739897 is 7989371991.

It can be written as a sum of positive squares in 4 ways, for example, as 577152576 + 1414587321 = 24024^2 + 37611^2 .

It is not a de Polignac number, because 1991739897 - 2⁴ = 1991739881 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (63).

It is not an unprimeable number, because it can be changed into a prime (1991739899) by changing a digit.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 4320247 + ... + 4320707.

It is an arithmetic number, because the mean of its divisors is an integer number (47528481).

Almost surely, 2^1991739897 is an apocalyptic number.

It is an amenable number.

1991739897 is a deficient number, since it is larger than the sum of its proper divisors (1430310735).

1991739897 is a wasteful number, since it uses less digits than its factorization.

1991739897 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 679 (or 669 counting only the distinct ones).

The product of its digits is 7715736, while the sum is 63.

The square root of 1991739897 is about 44628.9132401854. The cubic root of 1991739897 is about 1258.1841435842.

The spelling of 1991739897 in words is "one billion, nine hundred ninety-one million, seven hundred thirty-nine thousand, eight hundred ninety-seven".