261499778028 has 192 divisors, whose sum is σ = 769886208000. Its totient is φ = 76254317568.

The previous prime is 261499778003. The next prime is 261499778069. The reversal of 261499778028 is 820877994162.

261499778028 is a `hidden beast` number, since 2 + 61 + 499 + 7 + 7 + 80 + 2 + 8 = 666.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 1778133 + ... + 1919571.

It is an arithmetic number, because the mean of its divisors is an integer number (4009824000).

Almost surely, 2^261499778028 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 261499778028, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (384943104000).

261499778028 is an abundant number, since it is smaller than the sum of its proper divisors (508386429972).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

261499778028 is a wasteful number, since it uses less digits than its factorization.

261499778028 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 141541 (or 141533 counting only the distinct ones).

The product of its (nonzero) digits is 24385536, while the sum is 63.

The spelling of 261499778028 in words is "two hundred sixty-one billion, four hundred ninety-nine million, seven hundred seventy-eight thousand, twenty-eight".