1720421 has 2 divisors, whose sum is σ = 1720422. Its totient is φ = 1720420.

The previous prime is 1720399. The next prime is 1720427. The reversal of 1720421 is 1240271.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 972196 + 748225 = 986^2 + 865^2 .

It is an emirp because it is prime and its reverse (1240271) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1720421 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 1720421.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1720427) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 860210 + 860211.

It is an arithmetic number, because the mean of its divisors is an integer number (860211).

2^1720421 is an apocalyptic number.

It is an amenable number.

1720421 is a deficient number, since it is larger than the sum of its proper divisors (1).

1720421 is an equidigital number, since it uses as much as digits as its factorization.

1720421 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 112, while the sum is 17.

The square root of 1720421 is about 1311.6481997853. The cubic root of 1720421 is about 119.8243030656.

Adding to 1720421 its reverse (1240271), we get a palindrome (2960692).

The spelling of 1720421 in words is "one million, seven hundred twenty thousand, four hundred twenty-one".