251635661 has 2 divisors, whose sum is σ = 251635662. Its totient is φ = 251635660.

The previous prime is 251635589. The next prime is 251635687. The reversal of 251635661 is 166536152.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 139381636 + 112254025 = 11806^2 + 10595^2 .

It is a cyclic number.

It is not a de Polignac number, because 251635661 - 2¹⁰ = 251634637 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (251635061) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 125817830 + 125817831.

It is an arithmetic number, because the mean of its divisors is an integer number (125817831).

Almost surely, 2^251635661 is an apocalyptic number.

It is an amenable number.

251635661 is a deficient number, since it is larger than the sum of its proper divisors (1).

251635661 is an equidigital number, since it uses as much as digits as its factorization.

251635661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 32400, while the sum is 35.

The square root of 251635661 is about 15863.0281157161. The cubic root of 251635661 is about 631.3314086949.

The spelling of 251635661 in words is "two hundred fifty-one million, six hundred thirty-five thousand, six hundred sixty-one".