1215555551 has 4 divisors (see below), whose sum is σ = 1389206352. Its totient is φ = 1041904752.

The previous prime is 1215555547. The next prime is 1215555553. The reversal of 1215555551 is 1555555121.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1555555121 = 11927 ⋅130423.

It is not a de Polignac number, because 1215555551 - 2² = 1215555547 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1215555553) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 86825390 + ... + 86825403.

It is an arithmetic number, because the mean of its divisors is an integer number (347301588).

Almost surely, 2^1215555551 is an apocalyptic number.

1215555551 is a deficient number, since it is larger than the sum of its proper divisors (173650801).

1215555551 is an equidigital number, since it uses as much as digits as its factorization.

1215555551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 173650800.

The product of its digits is 31250, while the sum is 35.

The square root of 1215555551 is about 34864.8182413160. The cubic root of 1215555551 is about 1067.2306032427.

The spelling of 1215555551 in words is "one billion, two hundred fifteen million, five hundred fifty-five thousand, five hundred fifty-one".