261099538440 has 256 divisors, whose sum is σ = 873764236800. Its totient is φ = 61974528000.

The previous prime is 261099538363. The next prime is 261099538457. The reversal of 261099538440 is 44835990162.

It is a Cunningham number, because it is equal to 510979²-1.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 39853165 + ... + 39859715.

It is an arithmetic number, because the mean of its divisors is an integer number (3413141550).

Almost surely, 2^261099538440 is an apocalyptic number.

261099538440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 261099538440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (436882118400).

261099538440 is an abundant number, since it is smaller than the sum of its proper divisors (612664698360).

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

261099538440 is a wasteful number, since it uses less digits than its factorization.

261099538440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7488 (or 7484 counting only the distinct ones).

The product of its (nonzero) digits is 1866240, while the sum is 51.

The spelling of 261099538440 in words is "two hundred sixty-one billion, ninety-nine million, five hundred thirty-eight thousand, four hundred forty".