18991890 has 48 divisors (see below), whose sum is σ = 52287768. Its totient is φ = 4766208.

The previous prime is 18991879. The next prime is 18991891. The reversal of 18991890 is 9819981.

It can be written as a sum of positive squares in 4 ways, for example, as 15848361 + 3143529 = 3981^2 + 1773^2 .

It is a Harshad number since it is a multiple of its sum of digits (45).

It is not an unprimeable number, because it can be changed into a prime (18991891) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 4677 + ... + 7736.

Almost surely, 2^18991890 is an apocalyptic number.

18991890 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

18991890 is an abundant number, since it is smaller than the sum of its proper divisors (33295878).

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

18991890 is a wasteful number, since it uses less digits than its factorization.

18991890 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12443 (or 12440 counting only the distinct ones).

The product of its (nonzero) digits is 46656, while the sum is 45.

The square root of 18991890 is about 4357.9685634479. The cubic root of 18991890 is about 266.8021932631.

It can be divided in two parts, 18991 and 890, that added together give a square (19881 = 141²).

The spelling of 18991890 in words is "eighteen million, nine hundred ninety-one thousand, eight hundred ninety".