1668624781 has 2 divisors, whose sum is σ = 1668624782. Its totient is φ = 1668624780.

The previous prime is 1668624773. The next prime is 1668624809. The reversal of 1668624781 is 1874268661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1565784900 + 102839881 = 39570^2 + 10141^2 .

It is a cyclic number.

It is not a de Polignac number, because 1668624781 - 2³ = 1668624773 is a prime.

It is a super-2 number, since 2×1668624781² = 5568617319534595922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1668624721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 834312390 + 834312391.

It is an arithmetic number, because the mean of its divisors is an integer number (834312391).

Almost surely, 2^1668624781 is an apocalyptic number.

It is an amenable number.

1668624781 is a deficient number, since it is larger than the sum of its proper divisors (1).

1668624781 is an equidigital number, since it uses as much as digits as its factorization.

1668624781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 774144, while the sum is 49.

The square root of 1668624781 is about 40848.8039114978. The cubic root of 1668624781 is about 1186.0952400276.

The spelling of 1668624781 in words is "one billion, six hundred sixty-eight million, six hundred twenty-four thousand, seven hundred eighty-one".