1491009581 has 4 divisors (see below), whose sum is σ = 1509883200. Its totient is φ = 1472135964.

The previous prime is 1491009557. The next prime is 1491009587. The reversal of 1491009581 is 1859001941.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 1859001941 = 241 ⋅7713701.

It is a cyclic number.

It is not a de Polignac number, because 1491009581 - 2¹⁴ = 1490993197 is a prime.

It is a super-2 number, since 2×1491009581² = 4446219141267591122, 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 (1491009587) 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, 9436691 + ... + 9436848.

It is an arithmetic number, because the mean of its divisors is an integer number (377470800).

Almost surely, 2^1491009581 is an apocalyptic number.

It is an amenable number.

1491009581 is a deficient number, since it is larger than the sum of its proper divisors (18873619).

1491009581 is an equidigital number, since it uses as much as digits as its factorization.

1491009581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18873618.

The product of its (nonzero) digits is 12960, while the sum is 38.

The square root of 1491009581 is about 38613.5932153432. The cubic root of 1491009581 is about 1142.4226669035.

The spelling of 1491009581 in words is "one billion, four hundred ninety-one million, nine thousand, five hundred eighty-one".