1216661661 has 32 divisors (see below), whose sum is σ = 1917060480. Its totient is φ = 759967488.

The previous prime is 1216661573. The next prime is 1216661689. The reversal of 1216661661 is 1661666121.

It is a happy number.

It is not a de Polignac number, because 1216661661 - 2¹⁴ = 1216645277 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1216661461) 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, 98355 + ... + 110031.

It is an arithmetic number, because the mean of its divisors is an integer number (59908140).

Almost surely, 2^1216661661 is an apocalyptic number.

It is an amenable number.

1216661661 is a deficient number, since it is larger than the sum of its proper divisors (700398819).

1216661661 is a wasteful number, since it uses less digits than its factorization.

1216661661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11930 (or 11924 counting only the distinct ones).

The product of its digits is 15552, while the sum is 36.

The square root of 1216661661 is about 34880.6774733519. The cubic root of 1216661661 is about 1067.5542183886.

The spelling of 1216661661 in words is "one billion, two hundred sixteen million, six hundred sixty-one thousand, six hundred sixty-one".