1215256561 has 2 divisors, whose sum is σ = 1215256562. Its totient is φ = 1215256560.

The previous prime is 1215256547. The next prime is 1215256573. The reversal of 1215256561 is 1656525121.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1081160161 + 134096400 = 32881^2 + 11580^2 .

It is a cyclic number.

It is not a de Polignac number, because 1215256561 - 2⁵ = 1215256529 is a prime.

It is not a weakly prime, because it can be changed into another prime (1215256541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 607628280 + 607628281.

It is an arithmetic number, because the mean of its divisors is an integer number (607628281).

Almost surely, 2^1215256561 is an apocalyptic number.

It is an amenable number.

1215256561 is a deficient number, since it is larger than the sum of its proper divisors (1).

1215256561 is an equidigital number, since it uses as much as digits as its factorization.

1215256561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 18000, while the sum is 34.

The square root of 1215256561 is about 34860.5301307941. The cubic root of 1215256561 is about 1067.1430938884.

The spelling of 1215256561 in words is "one billion, two hundred fifteen million, two hundred fifty-six thousand, five hundred sixty-one".