1216425661 has 4 divisors (see below), whose sum is σ = 1327009824. Its totient is φ = 1105841500.

The previous prime is 1216425643. The next prime is 1216425697. The reversal of 1216425661 is 1665246121.

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.

It is a cyclic number.

It is not a de Polignac number, because 1216425661 - 2¹⁷ = 1216294589 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 (1216425611) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 55292065 + ... + 55292086.

It is an arithmetic number, because the mean of its divisors is an integer number (331752456).

Almost surely, 2^1216425661 is an apocalyptic number.

1216425661 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1216425661 is a deficient number, since it is larger than the sum of its proper divisors (110584163).

1216425661 is a wasteful number, since it uses less digits than its factorization.

1216425661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 110584162.

The product of its digits is 17280, while the sum is 34.

The square root of 1216425661 is about 34877.2943474691. The cubic root of 1216425661 is about 1067.4851882176.

The spelling of 1216425661 in words is "one billion, two hundred sixteen million, four hundred twenty-five thousand, six hundred sixty-one".