1216381 has 4 divisors (see below), whose sum is σ = 1221372. Its totient is φ = 1211392.

The previous prime is 1216379. The next prime is 1216387. The reversal of 1216381 is 1836121.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1836121 = 7 ⋅262303.

It can be written as a sum of positive squares in 2 ways, for example, as 793881 + 422500 = 891^2 + 650^2 .

It is a cyclic number.

It is not a de Polignac number, because 1216381 - 2¹ = 1216379 is a prime.

It is a super-2 number, since 2×1216381² = 2959165474322, which contains 22 as substring.

It is an alternating number because its digits alternate between odd and even.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1216387) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2110 + ... + 2623.

It is an arithmetic number, because the mean of its divisors is an integer number (305343).

2^1216381 is an apocalyptic number.

It is an amenable number.

1216381 is a deficient number, since it is larger than the sum of its proper divisors (4991).

1216381 is an equidigital number, since it uses as much as digits as its factorization.

1216381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4990.

The product of its digits is 288, while the sum is 22.

The square root of 1216381 is about 1102.8966406695. The cubic root of 1216381 is about 106.7472123838.

The spelling of 1216381 in words is "one million, two hundred sixteen thousand, three hundred eighty-one".