1216315661 has 16 divisors (see below), whose sum is σ = 1355568000. Its totient is φ = 1082030400.

The previous prime is 1216315657. The next prime is 1216315669. The reversal of 1216315661 is 1665136121.

It is not a de Polignac number, because 1216315661 - 2² = 1216315657 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 (1216315669) 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, 128975 + ... + 138083.

It is an arithmetic number, because the mean of its divisors is an integer number (84723000).

Almost surely, 2^1216315661 is an apocalyptic number.

1216315661 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1216315661 is a deficient number, since it is larger than the sum of its proper divisors (139252339).

1216315661 is a wasteful number, since it uses less digits than its factorization.

1216315661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9380.

The product of its digits is 6480, while the sum is 32.

The square root of 1216315661 is about 34875.7173546294. The cubic root of 1216315661 is about 1067.4530100873.

The spelling of 1216315661 in words is "one billion, two hundred sixteen million, three hundred fifteen thousand, six hundred sixty-one".