1216280661 has 4 divisors (see below), whose sum is σ = 1621707552. Its totient is φ = 810853772.

The previous prime is 1216280633. The next prime is 1216280699. The reversal of 1216280661 is 1660826121.

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: 1660826121 = 3 ⋅553608707.

It is a cyclic number.

It is not a de Polignac number, because 1216280661 - 2¹³ = 1216272469 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1216280161) 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 3 ways as a sum of consecutive naturals, for example, 202713441 + ... + 202713446.

It is an arithmetic number, because the mean of its divisors is an integer number (405426888).

Almost surely, 2^1216280661 is an apocalyptic number.

It is an amenable number.

1216280661 is a deficient number, since it is larger than the sum of its proper divisors (405426891).

1216280661 is an equidigital number, since it uses as much as digits as its factorization.

1216280661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 405426890.

The product of its (nonzero) digits is 6912, while the sum is 33.

The square root of 1216280661 is about 34875.2155692262. The cubic root of 1216280661 is about 1067.4427711844.

The spelling of 1216280661 in words is "one billion, two hundred sixteen million, two hundred eighty thousand, six hundred sixty-one".