61638991 has 8 divisors (see below), whose sum is σ = 65333520. Its totient is φ = 57952128.

The previous prime is 61638979. The next prime is 61639001. The reversal of 61638991 is 19983616.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 61638991 - 2⁵ = 61638959 is a prime.

It is a super-2 number, since 2×61638991² = 7598730422996162, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (61638931) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 29365 + ... + 31393.

It is an arithmetic number, because the mean of its divisors is an integer number (8166690).

Almost surely, 2^61638991 is an apocalyptic number.

61638991 is a deficient number, since it is larger than the sum of its proper divisors (3694529).

61638991 is a wasteful number, since it uses less digits than its factorization.

61638991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3833.

The product of its digits is 69984, while the sum is 43.

The square root of 61638991 is about 7851.0503119009. The cubic root of 61638991 is about 395.0194745512.

The spelling of 61638991 in words is "sixty-one million, six hundred thirty-eight thousand, nine hundred ninety-one".