1661815777 has 2 divisors, whose sum is σ = 1661815778. Its totient is φ = 1661815776.

The previous prime is 1661815763. The next prime is 1661815783. The reversal of 1661815777 is 7775181661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1524433936 + 137381841 = 39044^2 + 11721^2 .

It is a cyclic number.

It is not a de Polignac number, because 1661815777 - 2¹¹ = 1661813729 is a prime.

It is a super-2 number, since 2×1661815777² = 5523263353372227458, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 1661815777.

It is not a weakly prime, because it can be changed into another prime (1661815747) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 830907888 + 830907889.

It is an arithmetic number, because the mean of its divisors is an integer number (830907889).

Almost surely, 2^1661815777 is an apocalyptic number.

It is an amenable number.

1661815777 is a deficient number, since it is larger than the sum of its proper divisors (1).

1661815777 is an equidigital number, since it uses as much as digits as its factorization.

1661815777 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 493920, while the sum is 49.

The square root of 1661815777 is about 40765.3747315047. The cubic root of 1661815777 is about 1184.4797105873.

The spelling of 1661815777 in words is "one billion, six hundred sixty-one million, eight hundred fifteen thousand, seven hundred seventy-seven".