51021661 has 4 divisors (see below), whose sum is σ = 51111900. Its totient is φ = 50931424.

The previous prime is 51021637. The next prime is 51021667. The reversal of 51021661 is 16612015.

51021661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 11256025 + 39765636 = 3355^2 + 6306^2 .

It is a cyclic number.

It is not a de Polignac number, because 51021661 - 2⁷ = 51021533 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (51021667) 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, 44266 + ... + 45403.

It is an arithmetic number, because the mean of its divisors is an integer number (12777975).

Almost surely, 2^51021661 is an apocalyptic number.

It is an amenable number.

51021661 is a deficient number, since it is larger than the sum of its proper divisors (90239).

51021661 is an equidigital number, since it uses as much as digits as its factorization.

51021661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 90238.

The product of its (nonzero) digits is 360, while the sum is 22.

The square root of 51021661 is about 7142.9448408902. The cubic root of 51021661 is about 370.8954716504.

Adding to 51021661 its reverse (16612015), we get a palindrome (67633676).

The spelling of 51021661 in words is "fifty-one million, twenty-one thousand, six hundred sixty-one".