1664427781 has 4 divisors (see below), whose sum is σ = 1664813632. Its totient is φ = 1664041932.

The previous prime is 1664427773. The next prime is 1664427803. The reversal of 1664427781 is 1877244661.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1664427781 - 2³ = 1664427773 is a prime.

It is a super-2 number, since 2×1664427781² = 5540639676329167922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1664427481) 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, 186381 + ... + 195106.

It is an arithmetic number, because the mean of its divisors is an integer number (416203408).

Almost surely, 2^1664427781 is an apocalyptic number.

It is an amenable number.

1664427781 is a deficient number, since it is larger than the sum of its proper divisors (385851).

1664427781 is an equidigital number, since it uses as much as digits as its factorization.

1664427781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 385850.

The product of its digits is 451584, while the sum is 46.

The square root of 1664427781 is about 40797.3991940663. The cubic root of 1664427781 is about 1185.0999650991.

The spelling of 1664427781 in words is "one billion, six hundred sixty-four million, four hundred twenty-seven thousand, seven hundred eighty-one".