781987091661 has 6 divisors (see below), whose sum is σ = 1129536910190. Its totient is φ = 521324727768.

The previous prime is 781987091653. The next prime is 781987091723. The reversal of 781987091661 is 166190789187.

It can be written as a sum of positive squares in only one way, i.e., 468258278436 + 313728813225 = 684294^2 + 560115^2 .

It is not a de Polignac number, because 781987091661 - 2³ = 781987091653 is a prime.

It is a super-2 number, since 2×781987091661² (a number of 25 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (781987091861) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 43443727306 + ... + 43443727323.

Almost surely, 2^781987091661 is an apocalyptic number.

It is an amenable number.

781987091661 is a deficient number, since it is larger than the sum of its proper divisors (347549818529).

781987091661 is a wasteful number, since it uses less digits than its factorization.

781987091661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 86887454635 (or 86887454632 counting only the distinct ones).

The product of its (nonzero) digits is 9144576, while the sum is 63.

The spelling of 781987091661 in words is "seven hundred eighty-one billion, nine hundred eighty-seven million, ninety-one thousand, six hundred sixty-one".