1261217591 has 4 divisors (see below), whose sum is σ = 1262439552. Its totient is φ = 1259995632.

The previous prime is 1261217543. The next prime is 1261217653. The reversal of 1261217591 is 1957121621.

It is a happy number.

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 1261217591 - 2¹⁸ = 1260955447 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 (1261217291) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 609431 + ... + 611496.

It is an arithmetic number, because the mean of its divisors is an integer number (315609888).

Almost surely, 2^1261217591 is an apocalyptic number.

1261217591 is a deficient number, since it is larger than the sum of its proper divisors (1221961).

1261217591 is a wasteful number, since it uses less digits than its factorization.

1261217591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1221960.

The product of its digits is 7560, while the sum is 35.

The square root of 1261217591 is about 35513.6254274328. The cubic root of 1261217591 is about 1080.4300959011.

It can be divided in two parts, 12612 and 17591, that added together give a palindrome (30203).

The spelling of 1261217591 in words is "one billion, two hundred sixty-one million, two hundred seventeen thousand, five hundred ninety-one".