1551508991 has 4 divisors (see below), whose sum is σ = 1560799632. Its totient is φ = 1542218352.

The previous prime is 1551508979. The next prime is 1551508993. The reversal of 1551508991 is 1998051551.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1998051551 = 157 ⋅12726443.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1551508991 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1551508993) 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, 4645070 + ... + 4645403.

It is an arithmetic number, because the mean of its divisors is an integer number (390199908).

Almost surely, 2^1551508991 is an apocalyptic number.

1551508991 is a deficient number, since it is larger than the sum of its proper divisors (9290641).

1551508991 is an equidigital number, since it uses as much as digits as its factorization.

1551508991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9290640.

The product of its (nonzero) digits is 81000, while the sum is 44.

The square root of 1551508991 is about 39389.1989129000. The cubic root of 1551508991 is about 1157.6699639550.

The spelling of 1551508991 in words is "one billion, five hundred fifty-one million, five hundred eight thousand, nine hundred ninety-one".