1221100021 has 8 divisors (see below), whose sum is σ = 1293280344. Its totient is φ = 1148958720.

The previous prime is 1221099967. The next prime is 1221100033. The reversal of 1221100021 is 1200011221.

It can be written as a sum of positive squares in 4 ways, for example, as 471107025 + 749992996 = 21705^2 + 27386^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1221100021 - 2¹⁷ = 1220968949 is a prime.

It is a super-2 number, since 2×1221100021² = 2982170522572400882, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 1221099980 and 1221100007.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1221100121) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 76581 + ... + 91141.

It is an arithmetic number, because the mean of its divisors is an integer number (161660043).

Almost surely, 2^1221100021 is an apocalyptic number.

It is an amenable number.

1221100021 is a deficient number, since it is larger than the sum of its proper divisors (72180323).

1221100021 is a wasteful number, since it uses less digits than its factorization.

1221100021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19511.

The product of its (nonzero) digits is 8, while the sum is 10.

The square root of 1221100021 is about 34944.2416000119. The cubic root of 1221100021 is about 1068.8507826212.

Adding to 1221100021 its reverse (1200011221), we get a palindrome (2421111242).

The spelling of 1221100021 in words is "one billion, two hundred twenty-one million, one hundred thousand, twenty-one".