9781661 has 2 divisors, whose sum is σ = 9781662. Its totient is φ = 9781660.

The previous prime is 9781649. The next prime is 9781697. The reversal of 9781661 is 1661879.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 9672100 + 109561 = 3110^2 + 331^2 .

It is a cyclic number.

It is not a de Polignac number, because 9781661 - 2¹⁴ = 9765277 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (9781631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4890830 + 4890831.

It is an arithmetic number, because the mean of its divisors is an integer number (4890831).

Almost surely, 2^9781661 is an apocalyptic number.

It is an amenable number.

9781661 is a deficient number, since it is larger than the sum of its proper divisors (1).

9781661 is an equidigital number, since it uses as much as digits as its factorization.

9781661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 18144, while the sum is 38.

The square root of 9781661 is about 3127.5647075640. The cubic root of 9781661 is about 213.8639263635.

The spelling of 9781661 in words is "nine million, seven hundred eighty-one thousand, six hundred sixty-one".