2181961 has 4 divisors (see below), whose sum is σ = 2185924. Its totient is φ = 2178000.

The previous prime is 2181953. The next prime is 2181973. The reversal of 2181961 is 1691812.

2181961 = 1044² + 1045².

It is a happy number.

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 1092025 + 1089936 = 1045^2 + 1044^2 .

It is a 3-Lehmer number, since φ(2181961) divides (2181961-1)³.

It is a cyclic number.

It is not a de Polignac number, because 2181961 - 2³ = 2181953 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2181161) 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, 990 + ... + 2311.

It is an arithmetic number, because the mean of its divisors is an integer number (546481).

It is a Poulet number, since it divides 2^2181960-1.

2^2181961 is an apocalyptic number.

2181961 is the 1045-th centered square number.

It is an amenable number.

2181961 is a deficient number, since it is larger than the sum of its proper divisors (3963).

2181961 is an equidigital number, since it uses as much as digits as its factorization.

2181961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3962.

The product of its digits is 864, while the sum is 28.

The square root of 2181961 is about 1477.1462351440. The cubic root of 2181961 is about 129.7026933668.

The spelling of 2181961 in words is "two million, one hundred eighty-one thousand, nine hundred sixty-one".