661555506699 has 6 divisors (see below), whose sum is σ = 955580176356. Its totient is φ = 441037004460.

The previous prime is 661555506643. The next prime is 661555506779. The reversal of 661555506699 is 996605555166.

661555506699 is a `hidden beast` number, since 6 + 6 + 15 + 5 + 550 + 6 + 69 + 9 = 666.

It is not a de Polignac number, because 661555506699 - 2¹² = 661555502603 is a prime.

It is not an unprimeable number, because it can be changed into a prime (661555506499) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 36753083697 + ... + 36753083714.

It is an arithmetic number, because the mean of its divisors is an integer number (159263362726).

Almost surely, 2^661555506699 is an apocalyptic number.

661555506699 is a deficient number, since it is larger than the sum of its proper divisors (294024669657).

661555506699 is a wasteful number, since it uses less digits than its factorization.

661555506699 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 73506167417 (or 73506167414 counting only the distinct ones).

The product of its (nonzero) digits is 65610000, while the sum is 63.

The spelling of 661555506699 in words is "six hundred sixty-one billion, five hundred fifty-five million, five hundred six thousand, six hundred ninety-nine".