1921780 has 72 divisors (see below), whose sum is σ = 4912488. Its totient is φ = 628992.

The previous prime is 1921771. The next prime is 1921781. The reversal of 1921780 is 871291.

1921780 is a nontrivial binomial coefficient, being equal to C(1961, 2).

It can be written as a sum of positive squares in 4 ways, for example, as 729316 + 1192464 = 854^2 + 1092^2 .

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1921781) 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, 36234 + ... + 36286.

It is an arithmetic number, because the mean of its divisors is an integer number (68229).

2^1921780 is an apocalyptic number.

1921780 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

1921780 is the 1960-th triangular number.

1921780 is the 654-th centered nonagonal number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1921780, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2456244).

1921780 is an abundant number, since it is smaller than the sum of its proper divisors (2990708).

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

1921780 is a wasteful number, since it uses less digits than its factorization.

1921780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 113 (or 104 counting only the distinct ones).

The product of its (nonzero) digits is 1008, while the sum is 28.

The square root of 1921780 is about 1386.2827994316. The cubic root of 1921780 is about 124.3276972211.

1921780 divided by its sum of digits (28) gives a triangular number (68635 = T₃₇₀).

It can be divided in two parts, 1921 and 780, that added together give a triangular number (2701 = T₇₃).

The spelling of 1921780 in words is "one million, nine hundred twenty-one thousand, seven hundred eighty".