861091591 has 2 divisors, whose sum is σ = 861091592. Its totient is φ = 861091590.

The previous prime is 861091541. The next prime is 861091631. The reversal of 861091591 is 195190168.

It is an a-pointer prime, because the next prime (861091631) can be obtained adding 861091591 to its sum of digits (40).

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 861091591 - 2¹¹ = 861089543 is a prime.

It is a super-2 number, since 2×861091591² = 1482957456181822562, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (861091541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 430545795 + 430545796.

It is an arithmetic number, because the mean of its divisors is an integer number (430545796).

Almost surely, 2^861091591 is an apocalyptic number.

861091591 is a deficient number, since it is larger than the sum of its proper divisors (1).

861091591 is an equidigital number, since it uses as much as digits as its factorization.

861091591 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 19440, while the sum is 40.

The square root of 861091591 is about 29344.3621672034. The cubic root of 861091591 is about 951.3707234013.

The spelling of 861091591 in words is "eight hundred sixty-one million, ninety-one thousand, five hundred ninety-one".