1215381661 has 8 divisors (see below), whose sum is σ = 1344248024. Its totient is φ = 1091568960.

The previous prime is 1215381659. The next prime is 1215381701. The reversal of 1215381661 is 1661835121.

It can be written as a sum of positive squares in 4 ways, for example, as 353665636 + 861716025 = 18806^2 + 29355^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1215381661 - 2¹ = 1215381659 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 (1215381611) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1262910 + ... + 1263871.

It is an arithmetic number, because the mean of its divisors is an integer number (168031003).

Almost surely, 2^1215381661 is an apocalyptic number.

It is an amenable number.

1215381661 is a deficient number, since it is larger than the sum of its proper divisors (128866363).

1215381661 is a wasteful number, since it uses less digits than its factorization.

1215381661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2526831.

The product of its digits is 8640, while the sum is 34.

The square root of 1215381661 is about 34862.3243774709. The cubic root of 1215381661 is about 1067.1797103047.

The spelling of 1215381661 in words is "one billion, two hundred fifteen million, three hundred eighty-one thousand, six hundred sixty-one".