1661644757 has 2 divisors, whose sum is σ = 1661644758. Its totient is φ = 1661644756.

The previous prime is 1661644739. The next prime is 1661644763. The reversal of 1661644757 is 7574461661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1555986916 + 105657841 = 39446^2 + 10279^2 .

It is a cyclic number.

It is not a de Polignac number, because 1661644757 - 2⁶ = 1661644693 is a prime.

It is a super-2 number, since 2×1661644757² = 5522126596931178098, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1661644727) 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, 830822378 + 830822379.

It is an arithmetic number, because the mean of its divisors is an integer number (830822379).

Almost surely, 2^1661644757 is an apocalyptic number.

It is an amenable number.

1661644757 is a deficient number, since it is larger than the sum of its proper divisors (1).

1661644757 is an equidigital number, since it uses as much as digits as its factorization.

1661644757 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 846720, while the sum is 47.

The square root of 1661644757 is about 40763.2770640438. The cubic root of 1661644757 is about 1184.4390769880.

The spelling of 1661644757 in words is "one billion, six hundred sixty-one million, six hundred forty-four thousand, seven hundred fifty-seven".