1990855561 has 2 divisors, whose sum is σ = 1990855562. Its totient is φ = 1990855560.

The previous prime is 1990855553. The next prime is 1990855571. The reversal of 1990855561 is 1655580991.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1990855161 + 400 = 44619^2 + 20^2 .

It is a cyclic number.

It is not a de Polignac number, because 1990855561 - 2³ = 1990855553 is a prime.

It is not a weakly prime, because it can be changed into another prime (1990855571) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995427780 + 995427781.

It is an arithmetic number, because the mean of its divisors is an integer number (995427781).

Almost surely, 2^1990855561 is an apocalyptic number.

It is an amenable number.

1990855561 is a deficient number, since it is larger than the sum of its proper divisors (1).

1990855561 is an equidigital number, since it uses as much as digits as its factorization.

1990855561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 486000, while the sum is 49.

The square root of 1990855561 is about 44619.0044823952. The cubic root of 1990855561 is about 1257.9979040307.

The spelling of 1990855561 in words is "one billion, nine hundred ninety million, eight hundred fifty-five thousand, five hundred sixty-one".