19981657 has 4 divisors (see below), whose sum is σ = 20206260. Its totient is φ = 19757056.

The previous prime is 19981649. The next prime is 19981693. The reversal of 19981657 is 75618991.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 13278736 + 6702921 = 3644^2 + 2589^2 .

It is a cyclic number.

It is not a de Polignac number, because 19981657 - 2³ = 19981649 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19981697) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 112168 + ... + 112345.

It is an arithmetic number, because the mean of its divisors is an integer number (5051565).

Almost surely, 2^19981657 is an apocalyptic number.

It is an amenable number.

19981657 is a deficient number, since it is larger than the sum of its proper divisors (224603).

19981657 is an equidigital number, since it uses as much as digits as its factorization.

19981657 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 224602.

The product of its digits is 136080, while the sum is 46.

The square root of 19981657 is about 4470.0846748132. The cubic root of 19981657 is about 271.3587520063.

It can be divided in two parts, 1998 and 1657, that added together give a triangular number (3655 = T₈₅).

The spelling of 19981657 in words is "nineteen million, nine hundred eighty-one thousand, six hundred fifty-seven".