1216400661 has 48 divisors (see below), whose sum is σ = 2094496768. Its totient is φ = 665625600.

The previous prime is 1216400659. The next prime is 1216400663. The reversal of 1216400661 is 1660046121.

1216400661 is a `hidden beast` number, since 12 + 1 + 640 + 0 + 6 + 6 + 1 = 666.

It is an interprime number because it is at equal distance from previous prime (1216400659) and next prime (1216400663).

It is not a de Polignac number, because 1216400661 - 2¹ = 1216400659 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1216400663) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 186231 + ... + 192651.

Almost surely, 2^1216400661 is an apocalyptic number.

It is an amenable number.

1216400661 is a deficient number, since it is larger than the sum of its proper divisors (878096107).

1216400661 is a wasteful number, since it uses less digits than its factorization.

1216400661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6562 (or 6559 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 1216400661 is about 34876.9359462668. The cubic root of 1216400661 is about 1067.4778751765.

Adding to 1216400661 its reverse (1660046121), we get a palindrome (2876446782).

The spelling of 1216400661 in words is "one billion, two hundred sixteen million, four hundred thousand, six hundred sixty-one".