1661781 has 16 divisors (see below), whose sum is σ = 2484288. Its totient is φ = 979200.

The previous prime is 1661741. The next prime is 1661789. The reversal of 1661781 is 1871661.

It is a happy number.

It is not a de Polignac number, because 1661781 - 2¹⁵ = 1629013 is a prime.

It is a super-2 number, since 2×1661781² = 5523032183922, which contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1661789) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 541 + ... + 1901.

It is an arithmetic number, because the mean of its divisors is an integer number (155268).

2^1661781 is an apocalyptic number.

1661781 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1661781 is a deficient number, since it is larger than the sum of its proper divisors (822507).

1661781 is a wasteful number, since it uses less digits than its factorization.

1661781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1412.

The product of its digits is 2016, while the sum is 30.

The square root of 1661781 is about 1289.1008494296. The cubic root of 1661781 is about 118.4471447951.

It can be divided in two parts, 1661 and 781, that added together give a palindrome (2442).

The spelling of 1661781 in words is "one million, six hundred sixty-one thousand, seven hundred eighty-one".