1261217509 has 2 divisors, whose sum is σ = 1261217510. Its totient is φ = 1261217508.

The previous prime is 1261217497. The next prime is 1261217543. The reversal of 1261217509 is 9057121621.

It is an a-pointer prime, because the next prime (1261217543) can be obtained adding 1261217509 to its sum of digits (34).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 666930625 + 594286884 = 25825^2 + 24378^2 .

It is a cyclic number.

It is not a de Polignac number, because 1261217509 - 2⁷ = 1261217381 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1261217809) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 630608754 + 630608755.

It is an arithmetic number, because the mean of its divisors is an integer number (630608755).

Almost surely, 2^1261217509 is an apocalyptic number.

It is an amenable number.

1261217509 is a deficient number, since it is larger than the sum of its proper divisors (1).

1261217509 is an equidigital number, since it uses as much as digits as its factorization.

1261217509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 7560, while the sum is 34.

The square root of 1261217509 is about 35513.6242729463. The cubic root of 1261217509 is about 1080.4300724858.

The spelling of 1261217509 in words is "one billion, two hundred sixty-one million, two hundred seventeen thousand, five hundred nine".