1266155521 has 4 divisors (see below), whose sum is σ = 1266289200. Its totient is φ = 1266021844.

The previous prime is 1266155441. The next prime is 1266155551. The reversal of 1266155521 is 1255516621.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 1255516621 = 2663 ⋅471467.

It is a cyclic number.

It is not a de Polignac number, because 1266155521 - 2²⁵ = 1232601089 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1266155551) 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, 51451 + ... + 71968.

It is an arithmetic number, because the mean of its divisors is an integer number (316572300).

It is a Proth number, since it is equal to 2415 ⋅ 2¹⁹ + 1 and 2415 < 2¹⁹.

Almost surely, 2^1266155521 is an apocalyptic number.

It is an amenable number.

1266155521 is a deficient number, since it is larger than the sum of its proper divisors (133679).

1266155521 is a wasteful number, since it uses less digits than its factorization.

1266155521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 133678.

The product of its digits is 18000, while the sum is 34.

The square root of 1266155521 is about 35583.0791388266. The cubic root of 1266155521 is about 1081.8382961106.

The spelling of 1266155521 in words is "one billion, two hundred sixty-six million, one hundred fifty-five thousand, five hundred twenty-one".