1661220 has 72 divisors (see below), whose sum is σ = 5503680. Its totient is φ = 402240.

The previous prime is 1661173. The next prime is 1661237. The reversal of 1661220 is 221661.

It is a happy number.

1661220 is a `hidden beast` number, since 1 + 661 + 2 + 2 + 0 = 666.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 1661193 and 1661202.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1561 + ... + 2399.

It is an arithmetic number, because the mean of its divisors is an integer number (76440).

2^1661220 is an apocalyptic number.

1661220 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1661220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2751840).

1661220 is an abundant number, since it is smaller than the sum of its proper divisors (3842460).

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

1661220 is a wasteful number, since it uses less digits than its factorization.

1661220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 865 (or 860 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

The square root of 1661220 is about 1288.8832375355. The cubic root of 1661220 is about 118.4338144531.

Adding to 1661220 its reverse (221661), we get a palindrome (1882881).

It can be divided in two parts, 1661 and 220, that added together give a palindrome (1881).

The spelling of 1661220 in words is "one million, six hundred sixty-one thousand, two hundred twenty".