1991507989 has 4 divisors (see below), whose sum is σ = 1991597356. Its totient is φ = 1991418624.

The previous prime is 1991507941. The next prime is 1991508031. The reversal of 1991507989 is 9897051991.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 9897051991 = 107 ⋅92495813.

It can be written as a sum of positive squares in 2 ways, for example, as 497067025 + 1494440964 = 22295^2 + 38658^2 .

It is a cyclic number.

It is not a de Polignac number, because 1991507989 - 2¹¹ = 1991505941 is a prime.

It is a super-2 number, since 2×1991507989² = 7932208140501648242, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991507909) 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, 18967 + ... + 65899.

It is an arithmetic number, because the mean of its divisors is an integer number (497899339).

Almost surely, 2^1991507989 is an apocalyptic number.

It is an amenable number.

1991507989 is a deficient number, since it is larger than the sum of its proper divisors (89367).

1991507989 is an equidigital number, since it uses as much as digits as its factorization.

1991507989 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 89366.

The product of its (nonzero) digits is 1837080, while the sum is 58.

The square root of 1991507989 is about 44626.3149834265. The cubic root of 1991507989 is about 1258.1353095147.

The spelling of 1991507989 in words is "one billion, nine hundred ninety-one million, five hundred seven thousand, nine hundred eighty-nine".