1989721 has 2 divisors, whose sum is σ = 1989722. Its totient is φ = 1989720.

The previous prime is 1989683. The next prime is 1989769. The reversal of 1989721 is 1279891.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1243225 + 746496 = 1115^2 + 864^2 .

It is a cyclic number.

It is not a de Polignac number, because 1989721 - 2¹¹ = 1987673 is a prime.

It is a Chen prime.

It is an Ulam number.

1989721 is a lucky number.

It is not a weakly prime, because it can be changed into another prime (1989791) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 994860 + 994861.

It is an arithmetic number, because the mean of its divisors is an integer number (994861).

2^1989721 is an apocalyptic number.

It is an amenable number.

1989721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1989721 is an equidigital number, since it uses as much as digits as its factorization.

1989721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9072, while the sum is 37.

The square root of 1989721 is about 1410.5747055722. The cubic root of 1989721 is about 125.7758886762.

The spelling of 1989721 in words is "one million, nine hundred eighty-nine thousand, seven hundred twenty-one".