1291721 has 4 divisors (see below), whose sum is σ = 1295892. Its totient is φ = 1287552.

The previous prime is 1291691. The next prime is 1291783. The reversal of 1291721 is 1271921.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 313600 + 978121 = 560^2 + 989^2 .

It is a cyclic number.

It is not a de Polignac number, because 1291721 - 2¹⁸ = 1029577 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1291021) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1580 + ... + 2253.

It is an arithmetic number, because the mean of its divisors is an integer number (323973).

2^1291721 is an apocalyptic number.

It is an amenable number.

1291721 is a deficient number, since it is larger than the sum of its proper divisors (4171).

1291721 is an equidigital number, since it uses as much as digits as its factorization.

1291721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4170.

The product of its digits is 252, while the sum is 23.

The square root of 1291721 is about 1136.5390446439. The cubic root of 1291721 is about 108.9071116170.

The spelling of 1291721 in words is "one million, two hundred ninety-one thousand, seven hundred twenty-one".