991783727621 has 16 divisors (see below), whose sum is σ = 1055907000000. Its totient is φ = 928856750976.

The previous prime is 991783727581. The next prime is 991783727639. The reversal of 991783727621 is 126727387199.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-991783727621 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991783727021) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9670550 + ... + 9772568.

It is an arithmetic number, because the mean of its divisors is an integer number (65994187500).

Almost surely, 2^991783727621 is an apocalyptic number.

It is an amenable number.

991783727621 is a deficient number, since it is larger than the sum of its proper divisors (64123272379).

991783727621 is a wasteful number, since it uses less digits than its factorization.

991783727621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 107876.

The product of its digits is 16003008, while the sum is 62.

The spelling of 991783727621 in words is "nine hundred ninety-one billion, seven hundred eighty-three million, seven hundred twenty-seven thousand, six hundred twenty-one".