661918819 has 4 divisors (see below), whose sum is σ = 662033080. Its totient is φ = 661804560.

The previous prime is 661918811. The next prime is 661918837. The reversal of 661918819 is 918819166.

It is a happy number.

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 661918819 - 2³ = 661918811 is a prime.

It is a super-2 number, since 2×661918819² = 876273045892709522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661918811) 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, 47949 + ... + 60190.

It is an arithmetic number, because the mean of its divisors is an integer number (165508270).

Almost surely, 2^661918819 is an apocalyptic number.

661918819 is a deficient number, since it is larger than the sum of its proper divisors (114261).

661918819 is a wasteful number, since it uses less digits than its factorization.

661918819 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 114260.

The product of its digits is 186624, while the sum is 49.

The square root of 661918819 is about 25727.7830175863. The cubic root of 661918819 is about 871.5017086042.

The spelling of 661918819 in words is "six hundred sixty-one million, nine hundred eighteen thousand, eight hundred nineteen".