1661401661 has 2 divisors, whose sum is σ = 1661401662. Its totient is φ = 1661401660.

The previous prime is 1661401649. The next prime is 1661401663. The reversal of 1661401661 is 1661041661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1397339161 + 264062500 = 37381^2 + 16250^2 .

It is a cyclic number.

It is not a de Polignac number, because 1661401661 - 2¹⁴ = 1661385277 is a prime.

Together with 1661401663, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1661401663) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 830700830 + 830700831.

It is an arithmetic number, because the mean of its divisors is an integer number (830700831).

Almost surely, 2^1661401661 is an apocalyptic number.

It is an amenable number.

1661401661 is a deficient number, since it is larger than the sum of its proper divisors (1).

1661401661 is an equidigital number, since it uses as much as digits as its factorization.

1661401661 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5184, while the sum is 32.

The square root of 1661401661 is about 40760.2951534947. The cubic root of 1661401661 is about 1184.3813136498.

Subtracting from 1661401661 its reverse (1661041661), we obtain a square (360000 = 600²).

The spelling of 1661401661 in words is "one billion, six hundred sixty-one million, four hundred one thousand, six hundred sixty-one".