1211551220 has 72 divisors (see below), whose sum is σ = 2918305152. Its totient is φ = 421389760.

The previous prime is 1211551219. The next prime is 1211551267. The reversal of 1211551220 is 221551121.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a junction number, because it is equal to n+sod(n) for n = 1211551192 and 1211551201.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 44777 + ... + 66543.

It is an arithmetic number, because the mean of its divisors is an integer number (40532016).

Almost surely, 2^1211551220 is an apocalyptic number.

1211551220 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 1211551220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1459152576).

1211551220 is an abundant number, since it is smaller than the sum of its proper divisors (1706753932).

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

1211551220 is a wasteful number, since it uses less digits than its factorization.

1211551220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21821 (or 21808 counting only the distinct ones).

The product of its (nonzero) digits is 200, while the sum is 20.

The square root of 1211551220 is about 34807.3443399522. The cubic root of 1211551220 is about 1066.0574096673.

Subtracting from 1211551220 its reverse (221551121), we obtain a palindrome (990000099).

The spelling of 1211551220 in words is "one billion, two hundred eleven million, five hundred fifty-one thousand, two hundred twenty".