1661647081 has 2 divisors, whose sum is σ = 1661647082. Its totient is φ = 1661647080.

The previous prime is 1661647067. The next prime is 1661647087. The reversal of 1661647081 is 1807461661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1346229481 + 315417600 = 36691^2 + 17760^2 .

It is an emirp because it is prime and its reverse (1807461661) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1661647081 - 2⁵ = 1661647049 is a prime.

It is a super-2 number, since 2×1661647081² = 5522142043591641122, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (1661647087) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 830823540 + 830823541.

It is an arithmetic number, because the mean of its divisors is an integer number (830823541).

Almost surely, 2^1661647081 is an apocalyptic number.

It is an amenable number.

1661647081 is a deficient number, since it is larger than the sum of its proper divisors (1).

1661647081 is an equidigital number, since it uses as much as digits as its factorization.

1661647081 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 48384, while the sum is 40.

The square root of 1661647081 is about 40763.3055700835. The cubic root of 1661647081 is about 1184.4396291789.

The spelling of 1661647081 in words is "one billion, six hundred sixty-one million, six hundred forty-seven thousand, eighty-one".