1221515550 has 72 divisors (see below), whose sum is σ = 3294331560. Its totient is φ = 324494400.

The previous prime is 1221515549. The next prime is 1221515551. The reversal of 1221515550 is 555151221.

1221515550 is digitally balanced in base 4, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (1221515549) and next prime (1221515551).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1221515551) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 116005 + ... + 126095.

It is an arithmetic number, because the mean of its divisors is an integer number (45754605).

Almost surely, 2^1221515550 is an apocalyptic number.

1221515550 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is a practical number, because each smaller number is the sum of distinct divisors of 1221515550, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1647165780).

1221515550 is an abundant number, since it is smaller than the sum of its proper divisors (2072816010).

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

1221515550 is a wasteful number, since it uses less digits than its factorization.

1221515550 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10378 (or 10370 counting only the distinct ones).

The product of its (nonzero) digits is 2500, while the sum is 27.

The square root of 1221515550 is about 34950.1866947803. The cubic root of 1221515550 is about 1068.9720088707.

Adding to 1221515550 its reverse (555151221), we get a palindrome (1776666771).

The spelling of 1221515550 in words is "one billion, two hundred twenty-one million, five hundred fifteen thousand, five hundred fifty".