1561931291 has 4 divisors (see below), whose sum is σ = 1587536784. Its totient is φ = 1536325800.

The previous prime is 1561931279. The next prime is 1561931297. The reversal of 1561931291 is 1921391651.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 1561931291 - 2²² = 1557736987 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1561931297) 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, 12802655 + ... + 12802776.

It is an arithmetic number, because the mean of its divisors is an integer number (396884196).

Almost surely, 2^1561931291 is an apocalyptic number.

1561931291 is a deficient number, since it is larger than the sum of its proper divisors (25605493).

1561931291 is an equidigital number, since it uses as much as digits as its factorization.

1561931291 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25605492.

The product of its digits is 14580, while the sum is 38.

The square root of 1561931291 is about 39521.2764343461. The cubic root of 1561931291 is about 1160.2564066074.

The spelling of 1561931291 in words is "one billion, five hundred sixty-one million, nine hundred thirty-one thousand, two hundred ninety-one".