661555219 has 4 divisors (see below), whose sum is σ = 712444096. Its totient is φ = 610666344.

The previous prime is 661555217. The next prime is 661555241. The reversal of 661555219 is 912555166.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 661555219 - 2¹ = 661555217 is a prime.

It is a super-2 number, since 2×661555219² = 875310615572275922, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (661555217) 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, 25444419 + ... + 25444444.

It is an arithmetic number, because the mean of its divisors is an integer number (178111024).

Almost surely, 2^661555219 is an apocalyptic number.

661555219 is a deficient number, since it is larger than the sum of its proper divisors (50888877).

661555219 is a wasteful number, since it uses less digits than its factorization.

661555219 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 50888876.

The product of its digits is 81000, while the sum is 40.

The square root of 661555219 is about 25720.7157559816. The cubic root of 661555219 is about 871.3421039057.

The spelling of 661555219 in words is "six hundred sixty-one million, five hundred fifty-five thousand, two hundred nineteen".