1216766521 has 4 divisors (see below), whose sum is σ = 1217606544. Its totient is φ = 1215926500.

The previous prime is 1216766519. The next prime is 1216766531. The reversal of 1216766521 is 1256676121.

It is a happy number.

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.

It is a cyclic number.

It is not a de Polignac number, because 1216766521 - 2¹ = 1216766519 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1216766531) 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, 417835 + ... + 420736.

It is an arithmetic number, because the mean of its divisors is an integer number (304401636).

Almost surely, 2^1216766521 is an apocalyptic number.

It is an amenable number.

1216766521 is a deficient number, since it is larger than the sum of its proper divisors (840023).

1216766521 is an equidigital number, since it uses as much as digits as its factorization.

1216766521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 840022.

The product of its digits is 30240, while the sum is 37.

The square root of 1216766521 is about 34882.1805654406. The cubic root of 1216766521 is about 1067.5848871502.

The spelling of 1216766521 in words is "one billion, two hundred sixteen million, seven hundred sixty-six thousand, five hundred twenty-one".