1216155661 has 16 divisors (see below), whose sum is σ = 1409937408. Its totient is φ = 1027494000.

The previous prime is 1216155641. The next prime is 1216155671. The reversal of 1216155661 is 1665516121.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1216155661 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1216155641) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 134076 + ... + 142858.

It is an arithmetic number, because the mean of its divisors is an integer number (88121088).

Almost surely, 2^1216155661 is an apocalyptic number.

It is an amenable number.

1216155661 is a deficient number, since it is larger than the sum of its proper divisors (193781747).

1216155661 is a wasteful number, since it uses less digits than its factorization.

1216155661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9072.

The product of its digits is 10800, while the sum is 34.

The square root of 1216155661 is about 34873.4234195612. The cubic root of 1216155661 is about 1067.4062020706.

The spelling of 1216155661 in words is "one billion, two hundred sixteen million, one hundred fifty-five thousand, six hundred sixty-one".