1778221 has 2 divisors, whose sum is σ = 1778222. Its totient is φ = 1778220.

The previous prime is 1778219. The next prime is 1778239. The reversal of 1778221 is 1228771.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1232100 + 546121 = 1110^2 + 739^2 .

It is a cyclic number.

It is not a de Polignac number, because 1778221 - 2¹ = 1778219 is a prime.

Together with 1778219, it forms a pair of twin primes.

It is a Chen prime.

1778221 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 1778221.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1778261) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 889110 + 889111.

It is an arithmetic number, because the mean of its divisors is an integer number (889111).

2^1778221 is an apocalyptic number.

It is an amenable number.

1778221 is a deficient number, since it is larger than the sum of its proper divisors (1).

1778221 is an equidigital number, since it uses as much as digits as its factorization.

1778221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1568, while the sum is 28.

The square root of 1778221 is about 1333.4995313085. The cubic root of 1778221 is about 121.1514393718.

The spelling of 1778221 in words is "one million, seven hundred seventy-eight thousand, two hundred twenty-one".