1221100020 has 216 divisors, whose sum is σ = 4318763904. Its totient is φ = 273549312.

The previous prime is 1221099967. The next prime is 1221100033. The reversal of 1221100020 is 200011221.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a junction number, because it is equal to n+sod(n) for n = 1221099975 and 1221100011.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 11855289 + ... + 11855391.

Almost surely, 2^1221100020 is an apocalyptic number.

1221100020 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 1221100020, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2159381952).

1221100020 is an abundant number, since it is smaller than the sum of its proper divisors (3097663884).

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

1221100020 is a wasteful number, since it uses less digits than its factorization.

1221100020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 319 (or 217 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 9.

The square root of 1221100020 is about 34944.2415857034. The cubic root of 1221100020 is about 1068.8507823294.

Adding to 1221100020 its reverse (200011221), we get a palindrome (1421111241).

The spelling of 1221100020 in words is "one billion, two hundred twenty-one million, one hundred thousand, twenty".