1011555661 has 4 divisors (see below), whose sum is σ = 1012014972. Its totient is φ = 1011096352.

The previous prime is 1011555647. The next prime is 1011555679. The reversal of 1011555661 is 1665551101.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1665551101 = 1721 ⋅967781.

It can be written as a sum of positive squares in 2 ways, for example, as 1008062500 + 3493161 = 31750^2 + 1869^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1011555661 is a prime.

It is a super-2 number, since 2×1011555661² = 2046489710602293842, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1011555631) 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, 226336 + ... + 230761.

It is an arithmetic number, because the mean of its divisors is an integer number (253003743).

Almost surely, 2^1011555661 is an apocalyptic number.

It is an amenable number.

1011555661 is a deficient number, since it is larger than the sum of its proper divisors (459311).

1011555661 is an equidigital number, since it uses as much as digits as its factorization.

1011555661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 459310.

The product of its (nonzero) digits is 4500, while the sum is 31.

The square root of 1011555661 is about 31804.9628360104. The cubic root of 1011555661 is about 1003.8371444899.

The spelling of 1011555661 in words is "one billion, eleven million, five hundred fifty-five thousand, six hundred sixty-one".