251971561 has 2 divisors, whose sum is σ = 251971562. Its totient is φ = 251971560.

The previous prime is 251971553. The next prime is 251971567. The reversal of 251971561 is 165179152.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 206813161 + 45158400 = 14381^2 + 6720^2 .

It is a cyclic number.

It is not a de Polignac number, because 251971561 - 2³ = 251971553 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 251971561.

It is not a weakly prime, because it can be changed into another prime (251971567) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 125985780 + 125985781.

It is an arithmetic number, because the mean of its divisors is an integer number (125985781).

Almost surely, 2^251971561 is an apocalyptic number.

It is an amenable number.

251971561 is a deficient number, since it is larger than the sum of its proper divisors (1).

251971561 is an equidigital number, since it uses as much as digits as its factorization.

251971561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 18900, while the sum is 37.

The square root of 251971561 is about 15873.6120968102. The cubic root of 251971561 is about 631.6121981640.

The spelling of 251971561 in words is "two hundred fifty-one million, nine hundred seventy-one thousand, five hundred sixty-one".