1221520551 has 4 divisors (see below), whose sum is σ = 1628694072. Its totient is φ = 814347032.

The previous prime is 1221520529. The next prime is 1221520577. The reversal of 1221520551 is 1550251221.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 1221520551 - 2¹⁵ = 1221487783 is a prime.

It is a super-2 number, since 2×1221520551² = 2984224913030687202, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1221520511) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 203586756 + ... + 203586761.

It is an arithmetic number, because the mean of its divisors is an integer number (407173518).

Almost surely, 2^1221520551 is an apocalyptic number.

1221520551 is a deficient number, since it is larger than the sum of its proper divisors (407173521).

1221520551 is an equidigital number, since it uses as much as digits as its factorization.

1221520551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 407173520.

The product of its (nonzero) digits is 1000, while the sum is 24.

The square root of 1221520551 is about 34950.2582393893. The cubic root of 1221520551 is about 1068.9734676928.

Adding to 1221520551 its reverse (1550251221), we get a palindrome (2771771772).

The spelling of 1221520551 in words is "one billion, two hundred twenty-one million, five hundred twenty thousand, five hundred fifty-one".