1561989 has 24 divisors (see below), whose sum is σ = 2472736. Its totient is φ = 871200.

The previous prime is 1561919. The next prime is 1562051. The reversal of 1561989 is 9891651.

It is a de Polignac number, because none of the positive numbers 2^k-1561989 is a prime.

It is a super-2 number, since 2×1561989² = 4879619272242, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is an Ulam number.

It is a Duffinian number.

1561989 is a lucky number.

It is a nialpdrome in base 11.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1561919) 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, 4554 + ... + 4884.

2^1561989 is an apocalyptic number.

It is an amenable number.

1561989 is a deficient number, since it is larger than the sum of its proper divisors (910747).

1561989 is a wasteful number, since it uses less digits than its factorization.

1561989 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 369 (or 358 counting only the distinct ones).

The product of its digits is 19440, while the sum is 39.

The square root of 1561989 is about 1249.7955832855. The cubic root of 1561989 is about 116.0270695843.

Adding to 1561989 its sum of digits (39), we get a triangular number (1562028 = T₁₇₆₇).

It can be divided in two parts, 156 and 1989, that added together give a triangular number (2145 = T₆₅).

The spelling of 1561989 in words is "one million, five hundred sixty-one thousand, nine hundred eighty-nine".