155221220 has 192 divisors, whose sum is σ = 442713600. Its totient is φ = 45534720.

The previous prime is 155221219. The next prime is 155221223. The reversal of 155221220 is 22122551.

It is a happy number.

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 = 155221192 and 155221201.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (155221223) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 9130652 + ... + 9130668.

It is an arithmetic number, because the mean of its divisors is an integer number (2305800).

Almost surely, 2^155221220 is an apocalyptic number.

155221220 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 155221220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (221356800).

155221220 is an abundant number, since it is smaller than the sum of its proper divisors (287492380).

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

155221220 is a wasteful number, since it uses less digits than its factorization.

155221220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 80 (or 42 counting only the distinct ones).

The product of its (nonzero) digits is 400, while the sum is 20.

The square root of 155221220 is about 12458.7808392314. The cubic root of 155221220 is about 537.4239676120.

Adding to 155221220 its reverse (22122551), we get a palindrome (177343771).

The spelling of 155221220 in words is "one hundred fifty-five million, two hundred twenty-one thousand, two hundred twenty".