2151781 has 2 divisors, whose sum is σ = 2151782. Its totient is φ = 2151780.

The previous prime is 2151767. The next prime is 2151791. The reversal of 2151781 is 1871512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1232100 + 919681 = 1110^2 + 959^2 .

It is a cyclic number.

It is not a de Polignac number, because 2151781 - 2⁹ = 2151269 is a prime.

It is a super-2 number, since 2×2151781² = 9260322943922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2151701) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1075890 + 1075891.

It is an arithmetic number, because the mean of its divisors is an integer number (1075891).

2^2151781 is an apocalyptic number.

It is an amenable number.

2151781 is a deficient number, since it is larger than the sum of its proper divisors (1).

2151781 is an equidigital number, since it uses as much as digits as its factorization.

2151781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 560, while the sum is 25.

The square root of 2151781 is about 1466.8950201020. The cubic root of 2151781 is about 129.1019165351.

The spelling of 2151781 in words is "two million, one hundred fifty-one thousand, seven hundred eighty-one".