781685621 has 2 divisors, whose sum is σ = 781685622. Its totient is φ = 781685620.

The previous prime is 781685609. The next prime is 781685627. The reversal of 781685621 is 126586187.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 766514596 + 15171025 = 27686^2 + 3895^2 .

It is a cyclic number.

It is not a de Polignac number, because 781685621 - 2²² = 777491317 is a prime.

It is a super-2 number, since 2×781685621² = 1222064820156311282, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (781685627) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 390842810 + 390842811.

It is an arithmetic number, because the mean of its divisors is an integer number (390842811).

Almost surely, 2^781685621 is an apocalyptic number.

It is an amenable number.

781685621 is a deficient number, since it is larger than the sum of its proper divisors (1).

781685621 is an equidigital number, since it uses as much as digits as its factorization.

781685621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 161280, while the sum is 44.

The square root of 781685621 is about 27958.6412581155. The cubic root of 781685621 is about 921.1790259448.

The spelling of 781685621 in words is "seven hundred eighty-one million, six hundred eighty-five thousand, six hundred twenty-one".