1664546781 has 4 divisors (see below), whose sum is σ = 2219395712. Its totient is φ = 1109697852.

The previous prime is 1664546773. The next prime is 1664546837. The reversal of 1664546781 is 1876454661.

It is a happy number.

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, and also an emirpimes, since its reverse is a distinct semiprime: 1876454661 = 3 ⋅625484887.

It is not a de Polignac number, because 1664546781 - 2³ = 1664546773 is a prime.

It is a super-2 number, since 2×1664546781² = 5541431972274923922, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1664546781.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1664546701) 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, 277424461 + ... + 277424466.

It is an arithmetic number, because the mean of its divisors is an integer number (554848928).

Almost surely, 2^1664546781 is an apocalyptic number.

It is an amenable number.

1664546781 is a deficient number, since it is larger than the sum of its proper divisors (554848931).

1664546781 is an equidigital number, since it uses as much as digits as its factorization.

1664546781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 554848930.

The product of its digits is 967680, while the sum is 48.

The square root of 1664546781 is about 40798.8575943004. The cubic root of 1664546781 is about 1185.1282077453.

The spelling of 1664546781 in words is "one billion, six hundred sixty-four million, five hundred forty-six thousand, seven hundred eighty-one".