1215501561 has 12 divisors (see below), whose sum is σ = 1756523860. Its totient is φ = 809965440.

The previous prime is 1215501533. The next prime is 1215501571. The reversal of 1215501561 is 1651055121.

It can be written as a sum of positive squares in 2 ways, for example, as 712890000 + 502611561 = 26700^2 + 22419^2 .

It is not a de Polignac number, because 1215501561 - 2¹⁰ = 1215500537 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (1215501571) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 9076 + ... + 50133.

Almost surely, 2^1215501561 is an apocalyptic number.

It is an amenable number.

1215501561 is a deficient number, since it is larger than the sum of its proper divisors (541022299).

1215501561 is a wasteful number, since it uses less digits than its factorization.

1215501561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 61496 (or 61493 counting only the distinct ones).

The product of its (nonzero) digits is 1500, while the sum is 27.

The square root of 1215501561 is about 34864.0439564890. The cubic root of 1215501561 is about 1067.2148023377.

Adding to 1215501561 its reverse (1651055121), we get a palindrome (2866556682).

The spelling of 1215501561 in words is "one billion, two hundred fifteen million, five hundred one thousand, five hundred sixty-one".