691661251 has 2 divisors, whose sum is σ = 691661252. Its totient is φ = 691661250.

The previous prime is 691661227. The next prime is 691661293. The reversal of 691661251 is 152166196.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 691661251 - 2¹⁷ = 691530179 is a prime.

It is a super-2 number, since 2×691661251² = 956790572269770002, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 691661251.

It is not a weakly prime, because it can be changed into another prime (691661051) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 345830625 + 345830626.

It is an arithmetic number, because the mean of its divisors is an integer number (345830626).

Almost surely, 2^691661251 is an apocalyptic number.

691661251 is a deficient number, since it is larger than the sum of its proper divisors (1).

691661251 is an equidigital number, since it uses as much as digits as its factorization.

691661251 is an evil number, because the sum of its binary digits is even.

The product of its digits is 19440, while the sum is 37.

The square root of 691661251 is about 26299.4534353853. The cubic root of 691661251 is about 884.3641899248.

The spelling of 691661251 in words is "six hundred ninety-one million, six hundred sixty-one thousand, two hundred fifty-one".