1661989709 has 2 divisors, whose sum is σ = 1661989710. Its totient is φ = 1661989708.

The previous prime is 1661989687. The next prime is 1661989733. The reversal of 1661989709 is 9079891661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1422421225 + 239568484 = 37715^2 + 15478^2 .

It is a cyclic number.

It is not a de Polignac number, because 1661989709 - 2²⁴ = 1645212493 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1661989799) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 830994854 + 830994855.

It is an arithmetic number, because the mean of its divisors is an integer number (830994855).

Almost surely, 2^1661989709 is an apocalyptic number.

It is an amenable number.

1661989709 is a deficient number, since it is larger than the sum of its proper divisors (1).

1661989709 is an equidigital number, since it uses as much as digits as its factorization.

1661989709 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1469664, while the sum is 56.

The square root of 1661989709 is about 40767.5080057636. The cubic root of 1661989709 is about 1184.5210332058.

The spelling of 1661989709 in words is "one billion, six hundred sixty-one million, nine hundred eighty-nine thousand, seven hundred nine".