661556251 has 2 divisors, whose sum is σ = 661556252. Its totient is φ = 661556250.

The previous prime is 661556243. The next prime is 661556281. The reversal of 661556251 is 152655166.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 661556251 - 2³ = 661556243 is a prime.

It is a Chen prime.

It is equal to p_34362928 and since 661556251 and 34362928 have the same sum of digits, it is a Honaker prime.

It is a self number, because there is not a number n which added to its sum of digits gives 661556251.

It is not a weakly prime, because it can be changed into another prime (661556221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330778125 + 330778126.

It is an arithmetic number, because the mean of its divisors is an integer number (330778126).

Almost surely, 2^661556251 is an apocalyptic number.

661556251 is a deficient number, since it is larger than the sum of its proper divisors (1).

661556251 is an equidigital number, since it uses as much as digits as its factorization.

661556251 is an evil number, because the sum of its binary digits is even.

The product of its digits is 54000, while the sum is 37.

The square root of 661556251 is about 25720.7358176239. The cubic root of 661556251 is about 871.3425569918.

The spelling of 661556251 in words is "six hundred sixty-one million, five hundred fifty-six thousand, two hundred fifty-one".