2091557781 has 10 divisors (see below), whose sum is σ = 3124425942. Its totient is φ = 1394371800.

The previous prime is 2091557777. The next prime is 2091557789. The reversal of 2091557781 is 1877551902.

2091557781 is a `hidden beast` number, since 2 + 0 + 91 + 557 + 7 + 8 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 1614834225 + 476723556 = 40185^2 + 21834^2 .

It is not a de Polignac number, because 2091557781 - 2² = 2091557777 is a prime.

It is a super-2 number, since 2×2091557781² = 8749227902523287922, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2091557789) 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 9 ways as a sum of consecutive naturals, for example, 12910770 + ... + 12910931.

Almost surely, 2^2091557781 is an apocalyptic number.

It is an amenable number.

2091557781 is a deficient number, since it is larger than the sum of its proper divisors (1032868161).

2091557781 is an equidigital number, since it uses as much as digits as its factorization.

2091557781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25821713 (or 25821704 counting only the distinct ones).

The product of its (nonzero) digits is 176400, while the sum is 45.

The square root of 2091557781 is about 45733.5520269309. The cubic root of 2091557781 is about 1278.8608397142.

The spelling of 2091557781 in words is "two billion, ninety-one million, five hundred fifty-seven thousand, seven hundred eighty-one".