1555545661 has 2 divisors, whose sum is σ = 1555545662. Its totient is φ = 1555545660.

The previous prime is 1555545659. The next prime is 1555545671. The reversal of 1555545661 is 1665455551.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1179922500 + 375623161 = 34350^2 + 19381^2 .

It is a cyclic number.

It is not a de Polignac number, because 1555545661 - 2¹ = 1555545659 is a prime.

Together with 1555545659, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1555545631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 777772830 + 777772831.

It is an arithmetic number, because the mean of its divisors is an integer number (777772831).

Almost surely, 2^1555545661 is an apocalyptic number.

It is an amenable number.

1555545661 is a deficient number, since it is larger than the sum of its proper divisors (1).

1555545661 is an equidigital number, since it uses as much as digits as its factorization.

1555545661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 450000, while the sum is 43.

The square root of 1555545661 is about 39440.4064507454. The cubic root of 1555545661 is about 1158.6730915946.

It can be divided in two parts, 15555 and 45661, that added together give a palindrome (61216).

The spelling of 1555545661 in words is "one billion, five hundred fifty-five million, five hundred forty-five thousand, six hundred sixty-one".