1667625781 has 2 divisors, whose sum is σ = 1667625782. Its totient is φ = 1667625780.

The previous prime is 1667625679. The next prime is 1667625803. The reversal of 1667625781 is 1875267661.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1180540881 + 487084900 = 34359^2 + 22070^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1667625781 is a prime.

It is a super-2 number, since 2×1667625781² = 5561951490911719922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1667625181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 833812890 + 833812891.

It is an arithmetic number, because the mean of its divisors is an integer number (833812891).

Almost surely, 2^1667625781 is an apocalyptic number.

It is an amenable number.

1667625781 is a deficient number, since it is larger than the sum of its proper divisors (1).

1667625781 is an equidigital number, since it uses as much as digits as its factorization.

1667625781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 846720, while the sum is 49.

The square root of 1667625781 is about 40836.5740605159. The cubic root of 1667625781 is about 1185.8584890408.

The spelling of 1667625781 in words is "one billion, six hundred sixty-seven million, six hundred twenty-five thousand, seven hundred eighty-one".