1257721 has 2 divisors, whose sum is σ = 1257722. Its totient is φ = 1257720.

The previous prime is 1257719. The next prime is 1257749. The reversal of 1257721 is 1277521.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 746496 + 511225 = 864^2 + 715^2 .

It is a cyclic number.

It is not a de Polignac number, because 1257721 - 2¹ = 1257719 is a prime.

It is a super-2 number, since 2×1257721² = 3163724227682, which contains 22 as substring.

Together with 1257719, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (1257521) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 628860 + 628861.

It is an arithmetic number, because the mean of its divisors is an integer number (628861).

2^1257721 is an apocalyptic number.

It is an amenable number.

1257721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1257721 is an equidigital number, since it uses as much as digits as its factorization.

1257721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 980, while the sum is 25.

The square root of 1257721 is about 1121.4816093008. The cubic root of 1257721 is about 107.9430712774.

The spelling of 1257721 in words is "one million, two hundred fifty-seven thousand, seven hundred twenty-one".