1261405440 has 576 divisors, whose sum is σ = 5033145600. Its totient is φ = 297271296.

The previous prime is 1261405367. The next prime is 1261405477. The reversal of 1261405440 is 445041621.

1261405440 is a `hidden beast` number, since 1 + 2 + 614 + 0 + 5 + 4 + 40 = 666.

It is a tau number, because it is divible by the number of its divisors (576).

It is a super-2 number, since 2×1261405440² = 3182287368123187200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

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, 11162824 + ... + 11162936.

It is an arithmetic number, because the mean of its divisors is an integer number (8738100).

Almost surely, 2^1261405440 is an apocalyptic number.

1261405440 is a gapful number since it is divisible by the number (10) 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 1261405440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2516572800).

1261405440 is an abundant number, since it is smaller than the sum of its proper divisors (3771740160).

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

1261405440 is a wasteful number, since it uses less digits than its factorization.

1261405440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 179 (or 159 counting only the distinct ones).

The product of its (nonzero) digits is 3840, while the sum is 27.

The square root of 1261405440 is about 35516.2700744321. The cubic root of 1261405440 is about 1080.4837339197.

The spelling of 1261405440 in words is "one billion, two hundred sixty-one million, four hundred five thousand, four hundred forty".