15551221 has 8 divisors (see below), whose sum is σ = 18385920. Its totient is φ = 12869808.

The previous prime is 15551213. The next prime is 15551231. The reversal of 15551221 is 12215551.

It is a happy number.

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

It is not a de Polignac number, because 15551221 - 2³ = 15551213 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 15551192 and 15551201.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (15551231) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 38101 + ... + 38506.

It is an arithmetic number, because the mean of its divisors is an integer number (2298240).

Almost surely, 2^15551221 is an apocalyptic number.

It is an amenable number.

15551221 is a deficient number, since it is larger than the sum of its proper divisors (2834699).

15551221 is an equidigital number, since it uses as much as digits as its factorization.

15551221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 76643.

The product of its digits is 500, while the sum is 22.

The square root of 15551221 is about 3943.5036452373. The cubic root of 15551221 is about 249.6058910390.

Adding to 15551221 its reverse (12215551), we get a palindrome (27766772).

The spelling of 15551221 in words is "fifteen million, five hundred fifty-one thousand, two hundred twenty-one".