666221778 has 24 divisors (see below), whose sum is σ = 1482494988. Its totient is φ = 216071712.

The previous prime is 666221753. The next prime is 666221779. The reversal of 666221778 is 877122666.

It can be written as a sum of positive squares in 2 ways, for example, as 636704289 + 29517489 = 25233^2 + 5433^2 .

666221778 is a modest number, since divided by 221778 gives 666 as remainder.

It is not an unprimeable number, because it can be changed into a prime (666221779) 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, 499501 + ... + 500832.

Almost surely, 2^666221778 is an apocalyptic number.

666221778 is an abundant number, since it is smaller than the sum of its proper divisors (816273210).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

666221778 is a wasteful number, since it uses less digits than its factorization.

666221778 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1000378 (or 1000375 counting only the distinct ones).

The product of its digits is 338688, while the sum is 45.

The square root of 666221778 is about 25811.2723049446. The cubic root of 666221778 is about 873.3860984701.

The spelling of 666221778 in words is "six hundred sixty-six million, two hundred twenty-one thousand, seven hundred seventy-eight".