1261517661 has 18 divisors (see below), whose sum is σ = 1887204410. Its totient is φ = 812006496.

The previous prime is 1261517651. The next prime is 1261517669. The reversal of 1261517661 is 1667151621.

It is a happy number.

It can be written as a sum of positive squares in 3 ways, for example, as 274929561 + 986588100 = 16581^2 + 31410^2 .

It is not a de Polignac number, because 1261517661 - 2⁷ = 1261517533 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1261517669) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 75766 + ... + 90903.

Almost surely, 2^1261517661 is an apocalyptic number.

It is an amenable number.

1261517661 is a deficient number, since it is larger than the sum of its proper divisors (625686749).

1261517661 is a wasteful number, since it uses less digits than its factorization.

1261517661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 166733 (or 166701 counting only the distinct ones).

The product of its digits is 15120, while the sum is 36.

The square root of 1261517661 is about 35517.8498926948. The cubic root of 1261517661 is about 1080.5157747332.

It can be divided in two parts, 12615 and 17661, that added together give a square (30276 = 174²).

The spelling of 1261517661 in words is "one billion, two hundred sixty-one million, five hundred seventeen thousand, six hundred sixty-one".