1261521555 has 32 divisors (see below), whose sum is σ = 2309145600. Its totient is φ = 576104832.

The previous prime is 1261521553. The next prime is 1261521557. The reversal of 1261521555 is 5551251621.

It is an interprime number because it is at equal distance from previous prime (1261521553) and next prime (1261521557).

It is not a de Polignac number, because 1261521555 - 2¹ = 1261521553 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1261521553) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 106626 + ... + 117864.

It is an arithmetic number, because the mean of its divisors is an integer number (72160800).

Almost surely, 2^1261521555 is an apocalyptic number.

1261521555 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

1261521555 is a deficient number, since it is larger than the sum of its proper divisors (1047624045).

1261521555 is a wasteful number, since it uses less digits than its factorization.

1261521555 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12323.

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

The square root of 1261521555 is about 35517.9047101599. The cubic root of 1261521555 is about 1080.5168864957.

The spelling of 1261521555 in words is "one billion, two hundred sixty-one million, five hundred twenty-one thousand, five hundred fifty-five".