691402781 has 2 divisors, whose sum is σ = 691402782. Its totient is φ = 691402780.

The previous prime is 691402771. The next prime is 691402787. The reversal of 691402781 is 187204196.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 634536100 + 56866681 = 25190^2 + 7541^2 .

It is a cyclic number.

It is not a de Polignac number, because 691402781 - 2²² = 687208477 is a prime.

It is a super-2 number, since 2×691402781² = 956075611149067922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (691402787) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 345701390 + 345701391.

It is an arithmetic number, because the mean of its divisors is an integer number (345701391).

Almost surely, 2^691402781 is an apocalyptic number.

It is an amenable number.

691402781 is a deficient number, since it is larger than the sum of its proper divisors (1).

691402781 is an equidigital number, since it uses as much as digits as its factorization.

691402781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 24192, while the sum is 38.

The square root of 691402781 is about 26294.5389957687. The cubic root of 691402781 is about 884.2540155241.

The spelling of 691402781 in words is "six hundred ninety-one million, four hundred two thousand, seven hundred eighty-one".