1213721 has 2 divisors, whose sum is σ = 1213722. Its totient is φ = 1213720.

The previous prime is 1213673. The next prime is 1213741. The reversal of 1213721 is 1273121.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1210000 + 3721 = 1100^2 + 61^2 .

It is an emirp because it is prime and its reverse (1273121) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1213721 - 2⁶ = 1213657 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 1213721.

It is not a weakly prime, because it can be changed into another prime (1213741) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 606860 + 606861.

It is an arithmetic number, because the mean of its divisors is an integer number (606861).

2^1213721 is an apocalyptic number.

It is an amenable number.

1213721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1213721 is an equidigital number, since it uses as much as digits as its factorization.

1213721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 84, while the sum is 17.

The square root of 1213721 is about 1101.6900653088. The cubic root of 1213721 is about 106.6693434658.

Adding to 1213721 its reverse (1273121), we get a palindrome (2486842).

It can be divided in two parts, 121 and 3721, that multiplied together give a square (450241 = 671²).

The spelling of 1213721 in words is "one million, two hundred thirteen thousand, seven hundred twenty-one".