1643351220 has 288 divisors, whose sum is σ = 5998406400. Its totient is φ = 372411648.

The previous prime is 1643351209. The next prime is 1643351221. The reversal of 1643351220 is 221533461.

1643351220 is a `hidden beast` number, since 1 + 6 + 433 + 5 + 1 + 220 = 666.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1643351221) by changing a digit.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 4577401 + ... + 4577759.

It is an arithmetic number, because the mean of its divisors is an integer number (20827800).

Almost surely, 2^1643351220 is an apocalyptic number.

1643351220 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1643351220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2999203200).

1643351220 is an abundant number, since it is smaller than the sum of its proper divisors (4355055180).

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

1643351220 is a wasteful number, since it uses less digits than its factorization.

1643351220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 564 (or 549 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 27.

The square root of 1643351220 is about 40538.2685866084. The cubic root of 1643351220 is about 1180.0764146626.

Adding to 1643351220 its reverse (221533461), we get a palindrome (1864884681).

The spelling of 1643351220 in words is "one billion, six hundred forty-three million, three hundred fifty-one thousand, two hundred twenty".