51221220 has 24 divisors (see below), whose sum is σ = 143419584. Its totient is φ = 13658976.

The previous prime is 51221201. The next prime is 51221231. The reversal of 51221220 is 2212215.

It is a super-2 number, since 2×51221220² = 5247226756576800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 51221220.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 426784 + ... + 426903.

It is an arithmetic number, because the mean of its divisors is an integer number (5975816).

Almost surely, 2^51221220 is an apocalyptic number.

It is an amenable number.

51221220 is an abundant number, since it is smaller than the sum of its proper divisors (92198364).

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

51221220 is a wasteful number, since it uses less digits than its factorization.

51221220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 853699 (or 853697 counting only the distinct ones).

The product of its (nonzero) digits is 80, while the sum is 15.

The square root of 51221220 is about 7156.9001669717. The cubic root of 51221220 is about 371.3783988302.

Adding to 51221220 its reverse (2212215), we get a palindrome (53433435).

The spelling of 51221220 in words is "fifty-one million, two hundred twenty-one thousand, two hundred twenty".