1225566721 has 2 divisors, whose sum is σ = 1225566722. Its totient is φ = 1225566720.

The previous prime is 1225566659. The next prime is 1225566761. The reversal of 1225566721 is 1276655221.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 914397121 + 311169600 = 30239^2 + 17640^2 .

It is an emirp because it is prime and its reverse (1276655221) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1225566721 - 2¹¹ = 1225564673 is a prime.

It is not a weakly prime, because it can be changed into another prime (1225566761) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 612783360 + 612783361.

It is an arithmetic number, because the mean of its divisors is an integer number (612783361).

Almost surely, 2^1225566721 is an apocalyptic number.

It is an amenable number.

1225566721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1225566721 is an equidigital number, since it uses as much as digits as its factorization.

1225566721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 50400, while the sum is 37.

The square root of 1225566721 is about 35008.0950781387. The cubic root of 1225566721 is about 1070.1524576776.

The spelling of 1225566721 in words is "one billion, two hundred twenty-five million, five hundred sixty-six thousand, seven hundred twenty-one".