55991661 has 12 divisors (see below), whose sum is σ = 82059936. Its totient is φ = 33934120.

The previous prime is 55991603. The next prime is 55991669. The reversal of 55991661 is 16619955.

It is not a de Polignac number, because 55991661 - 2¹⁰ = 55990637 is a prime.

It is a super-2 number, since 2×55991661² = 6270132203077842, which contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (55991669) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 76761 + ... + 77486.

It is an arithmetic number, because the mean of its divisors is an integer number (6838328).

Almost surely, 2^55991661 is an apocalyptic number.

It is an amenable number.

55991661 is a deficient number, since it is larger than the sum of its proper divisors (26068275).

55991661 is a wasteful number, since it uses less digits than its factorization.

55991661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 154272 (or 154261 counting only the distinct ones).

The product of its digits is 72900, while the sum is 42.

The square root of 55991661 is about 7482.7575799300. The cubic root of 55991661 is about 382.5672452152.

It can be divided in two parts, 5599 and 1661, that added together give a triangular number (7260 = T₁₂₀).

The spelling of 55991661 in words is "fifty-five million, nine hundred ninety-one thousand, six hundred sixty-one".