991651 has 2 divisors, whose sum is σ = 991652. Its totient is φ = 991650.

The previous prime is 991643. The next prime is 991663. The reversal of 991651 is 156199.

991651 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 991651 - 2³ = 991643 is a prime.

It is not a weakly prime, because it can be changed into another prime (991621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495825 + 495826.

It is an arithmetic number, because the mean of its divisors is an integer number (495826).

2⁹⁹¹⁶⁵¹ is an apocalyptic number.

991651 is a deficient number, since it is larger than the sum of its proper divisors (1).

991651 is an equidigital number, since it uses as much as digits as its factorization.

991651 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2430, while the sum is 31.

The square root of 991651 is about 995.8167502106. The cubic root of 991651 is about 99.7209218786.

The spelling of 991651 in words is "nine hundred ninety-one thousand, six hundred fifty-one".