1781921 has 2 divisors, whose sum is σ = 1781922. Its totient is φ = 1781920.

The previous prime is 1781903. The next prime is 1781939. The reversal of 1781921 is 1291871.

It is a balanced prime because it is at equal distance from previous prime (1781903) and next prime (1781939).

It can be written as a sum of positive squares in only one way, i.e., 1234321 + 547600 = 1111^2 + 740^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1781921 is a prime.

It is not a weakly prime, because it can be changed into another prime (1781981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 890960 + 890961.

It is an arithmetic number, because the mean of its divisors is an integer number (890961).

2^1781921 is an apocalyptic number.

It is an amenable number.

1781921 is a deficient number, since it is larger than the sum of its proper divisors (1).

1781921 is an equidigital number, since it uses as much as digits as its factorization.

1781921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1008, while the sum is 29.

The square root of 1781921 is about 1334.8861374664. The cubic root of 1781921 is about 121.2354090211.

The spelling of 1781921 in words is "one million, seven hundred eighty-one thousand, nine hundred twenty-one".