991709639 has 2 divisors, whose sum is σ = 991709640. Its totient is φ = 991709638.

The previous prime is 991709597. The next prime is 991709683. The reversal of 991709639 is 936907199.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-991709639 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991709339) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495854819 + 495854820.

It is an arithmetic number, because the mean of its divisors is an integer number (495854820).

Almost surely, 2^991709639 is an apocalyptic number.

991709639 is a deficient number, since it is larger than the sum of its proper divisors (1).

991709639 is an equidigital number, since it uses as much as digits as its factorization.

991709639 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 826686, while the sum is 53.

The square root of 991709639 is about 31491.4216732113. The cubic root of 991709639 is about 997.2288742889.

The spelling of 991709639 in words is "nine hundred ninety-one million, seven hundred nine thousand, six hundred thirty-nine".