61821991 has 16 divisors (see below), whose sum is σ = 81135360. Its totient is φ = 45636480.

The previous prime is 61821983. The next prime is 61822001. The reversal of 61821991 is 19912816.

It is not a de Polignac number, because 61821991 - 2³ = 61821983 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 61821991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (61821941) 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, 19666 + ... + 22591.

It is an arithmetic number, because the mean of its divisors is an integer number (5070960).

Almost surely, 2^61821991 is an apocalyptic number.

61821991 is a deficient number, since it is larger than the sum of its proper divisors (19313369).

61821991 is a wasteful number, since it uses less digits than its factorization.

61821991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42294.

The product of its digits is 7776, while the sum is 37.

The square root of 61821991 is about 7862.6961660743. The cubic root of 61821991 is about 395.4100127547.

The spelling of 61821991 in words is "sixty-one million, eight hundred twenty-one thousand, nine hundred ninety-one".