51721661 has 4 divisors (see below), whose sum is σ = 52254972. Its totient is φ = 51188352.

The previous prime is 51721643. The next prime is 51721669. The reversal of 51721661 is 16612715.

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 35164900 + 16556761 = 5930^2 + 4069^2 .

It is a cyclic number.

It is not a de Polignac number, because 51721661 - 2¹⁰ = 51720637 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (51721669) 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, 266510 + ... + 266703.

It is an arithmetic number, because the mean of its divisors is an integer number (13063743).

Almost surely, 2^51721661 is an apocalyptic number.

It is an amenable number.

51721661 is a deficient number, since it is larger than the sum of its proper divisors (533311).

51721661 is an equidigital number, since it uses as much as digits as its factorization.

51721661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 533310.

The product of its digits is 2520, while the sum is 29.

The square root of 51721661 is about 7191.7773185771. Note that the first 3 decimals coincide. The cubic root of 51721661 is about 372.5839601743.

The spelling of 51721661 in words is "fifty-one million, seven hundred twenty-one thousand, six hundred sixty-one".