251601661 has 2 divisors, whose sum is σ = 251601662. Its totient is φ = 251601660.

The previous prime is 251601659. The next prime is 251601671. The reversal of 251601661 is 166106152.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 157628025 + 93973636 = 12555^2 + 9694^2 .

It is a cyclic number.

It is not a de Polignac number, because 251601661 - 2¹ = 251601659 is a prime.

Together with 251601659, it forms a pair of twin primes.

It is equal to p_13762225 and since 251601661 and 13762225 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (251601631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 125800830 + 125800831.

It is an arithmetic number, because the mean of its divisors is an integer number (125800831).

Almost surely, 2^251601661 is an apocalyptic number.

It is an amenable number.

251601661 is a deficient number, since it is larger than the sum of its proper divisors (1).

251601661 is an equidigital number, since it uses as much as digits as its factorization.

251601661 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2160, while the sum is 28.

The square root of 251601661 is about 15861.9564051853. The cubic root of 251601661 is about 631.3029730926.

The spelling of 251601661 in words is "two hundred fifty-one million, six hundred one thousand, six hundred sixty-one".