51661620 has 72 divisors (see below), whose sum is σ = 160962984. Its totient is φ = 13402368.

The previous prime is 51661613. The next prime is 51661637. The reversal of 51661620 is 2616615.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 22695696 + 28965924 = 4764^2 + 5382^2 .

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 2782 + ... + 10538.

It is an arithmetic number, because the mean of its divisors is an integer number (2235597).

Almost surely, 2^51661620 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 51661620, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (80481492).

51661620 is an abundant number, since it is smaller than the sum of its proper divisors (109301364).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

51661620 is a wasteful number, since it uses less digits than its factorization.

51661620 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7809 (or 7804 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The square root of 51661620 is about 7187.6018253657. The cubic root of 51661620 is about 372.4397332045.

It can be divided in two parts, 516616 and 20, that added together give a triangular number (516636 = T₁₀₁₆).

The spelling of 51661620 in words is "fifty-one million, six hundred sixty-one thousand, six hundred twenty".