261691920 has 240 divisors, whose sum is σ = 1014399360. Its totient is φ = 59222016.

The previous prime is 261691901. The next prime is 261691939. The reversal of 261691920 is 29196162.

261691920 is a `hidden beast` number, since 2 + 616 + 9 + 19 + 20 = 666.

It is an interprime number because it is at equal distance from previous prime (261691901) and next prime (261691939).

It is a tau number, because it is divible by the number of its divisors (240).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 690291 + ... + 690669.

It is an arithmetic number, because the mean of its divisors is an integer number (4226664).

Almost surely, 2^261691920 is an apocalyptic number.

261691920 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 261691920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (507199680).

261691920 is an abundant number, since it is smaller than the sum of its proper divisors (752707440).

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

261691920 is a wasteful number, since it uses less digits than its factorization.

261691920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 542 (or 533 counting only the distinct ones).

The product of its (nonzero) digits is 11664, while the sum is 36.

The square root of 261691920 is about 16176.8946340143. The cubic root of 261691920 is about 639.6318846621.

The spelling of 261691920 in words is "two hundred sixty-one million, six hundred ninety-one thousand, nine hundred twenty".