1221556551 has 8 divisors (see below), whose sum is σ = 1629884400. Its totient is φ = 813799872.

The previous prime is 1221556541. The next prime is 1221556559. The reversal of 1221556551 is 1556551221.

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

It is not a de Polignac number, because 1221556551 - 2⁶ = 1221556487 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1221556559) 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 7 ways as a sum of consecutive naturals, for example, 137776 + ... + 146373.

It is an arithmetic number, because the mean of its divisors is an integer number (203735550).

Almost surely, 2^1221556551 is an apocalyptic number.

1221556551 is a deficient number, since it is larger than the sum of its proper divisors (408327849).

1221556551 is a wasteful number, since it uses less digits than its factorization.

1221556551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 285585.

The product of its digits is 15000, while the sum is 33.

The square root of 1221556551 is about 34950.7732532486. The cubic root of 1221556551 is about 1068.9839689943.

The spelling of 1221556551 in words is "one billion, two hundred twenty-one million, five hundred fifty-six thousand, five hundred fifty-one".