27991638 has 12 divisors (see below), whose sum is σ = 60648588. Its totient is φ = 9330540.

The previous prime is 27991637. The next prime is 27991651. The reversal of 27991638 is 83619972.

27991638 is a `hidden beast` number, since 2 + 7 + 9 + 9 + 1 + 638 = 666.

It is a junction number, because it is equal to n+sod(n) for n = 27991593 and 27991602.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (27991633) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 777528 + ... + 777563.

It is an arithmetic number, because the mean of its divisors is an integer number (5054049).

Almost surely, 2^27991638 is an apocalyptic number.

27991638 is an abundant number, since it is smaller than the sum of its proper divisors (32656950).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

27991638 is a wasteful number, since it uses less digits than its factorization.

27991638 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1555099 (or 1555096 counting only the distinct ones).

The product of its digits is 163296, while the sum is 45.

The square root of 27991638 is about 5290.7124283975. The cubic root of 27991638 is about 303.6286656577.

The spelling of 27991638 in words is "twenty-seven million, nine hundred ninety-one thousand, six hundred thirty-eight".