2121451781 has 2 divisors, whose sum is σ = 2121451782. Its totient is φ = 2121451780.

The previous prime is 2121451747. The next prime is 2121451817. The reversal of 2121451781 is 1871541212.

Together with next prime (2121451817) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 2107269025 + 14182756 = 45905^2 + 3766^2 .

It is a cyclic number.

It is not a de Polignac number, because 2121451781 - 2²² = 2117257477 is a prime.

It is a super-2 number, since 2×2121451781² = 9001115318216143922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2121451681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1060725890 + 1060725891.

It is an arithmetic number, because the mean of its divisors is an integer number (1060725891).

Almost surely, 2^2121451781 is an apocalyptic number.

It is an amenable number.

2121451781 is a deficient number, since it is larger than the sum of its proper divisors (1).

2121451781 is an equidigital number, since it uses as much as digits as its factorization.

2121451781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4480, while the sum is 32.

The square root of 2121451781 is about 46059.2203689989. The cubic root of 2121451781 is about 1284.9248303972.

Adding to 2121451781 its reverse (1871541212), we get a palindrome (3992992993).

The spelling of 2121451781 in words is "two billion, one hundred twenty-one million, four hundred fifty-one thousand, seven hundred eighty-one".