51981221 has 2 divisors, whose sum is σ = 51981222. Its totient is φ = 51981220.

The previous prime is 51981199. The next prime is 51981247. The reversal of 51981221 is 12218915.

51981221 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 49773025 + 2208196 = 7055^2 + 1486^2 .

It is a cyclic number.

It is not a de Polignac number, because 51981221 - 2¹⁰ = 51980197 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (51981271) 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 as a sum of consecutive naturals, namely, 25990610 + 25990611.

It is an arithmetic number, because the mean of its divisors is an integer number (25990611).

Almost surely, 2^51981221 is an apocalyptic number.

It is an amenable number.

51981221 is a deficient number, since it is larger than the sum of its proper divisors (1).

51981221 is an equidigital number, since it uses as much as digits as its factorization.

51981221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1440, while the sum is 29.

The square root of 51981221 is about 7209.8003439762. The cubic root of 51981221 is about 373.2061789725.

The spelling of 51981221 in words is "fifty-one million, nine hundred eighty-one thousand, two hundred twenty-one".