991663109 has 2 divisors, whose sum is σ = 991663110. Its totient is φ = 991663108.

The previous prime is 991663103. The next prime is 991663121. The reversal of 991663109 is 901366199.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 976375009 + 15288100 = 31247^2 + 3910^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-991663109 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 991663109.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991663103) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495831554 + 495831555.

It is an arithmetic number, because the mean of its divisors is an integer number (495831555).

Almost surely, 2^991663109 is an apocalyptic number.

It is an amenable number.

991663109 is a deficient number, since it is larger than the sum of its proper divisors (1).

991663109 is an equidigital number, since it uses as much as digits as its factorization.

991663109 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 78732, while the sum is 44.

The square root of 991663109 is about 31490.6828919285. The cubic root of 991663109 is about 997.2132777260.

The spelling of 991663109 in words is "nine hundred ninety-one million, six hundred sixty-three thousand, one hundred nine".