21781738402281 has 405 divisors, whose sum is σ = 40107991706055. Its totient is φ = 11384715101760.

The previous prime is 21781738402279. The next prime is 21781738402301. The reversal of 21781738402281 is 18220483718712.

The square root of 21781738402281 is 4667091.

It is a perfect power (a square), and thus also a powerful number.

21781738402281 is a `hidden beast` number, since 2 + 17 + 81 + 73 + 8 + 402 + 2 + 81 = 666.

It can be written as a sum of positive squares in only one way, i.e., 3222150651225 + 18559587751056 = 1795035^2 + 4308084^2 .

It is not a de Polignac number, because 21781738402281 - 2¹ = 21781738402279 is a prime.

It is a super-2 number, since 2×21781738402281² (a number of 27 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21781738401281) by changing a digit.

It is a polite number, since it can be written in 404 ways as a sum of consecutive naturals, for example, 506552055846 + ... + 506552055888.

Almost surely, 2^{21781738402281} is an apocalyptic number.

21781738402281 is the 4667091-st square number.

21781738402281 is the 2333546-th centered octagonal number.

It is an amenable number.

21781738402281 is a deficient number, since it is larger than the sum of its proper divisors (18326253303774).

21781738402281 is an equidigital number, since it uses as much as digits as its factorization.

21781738402281 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 208 (or 93 counting only the distinct ones).

The product of its (nonzero) digits is 2408448, while the sum is 54.

The spelling of 21781738402281 in words is "twenty-one trillion, seven hundred eighty-one billion, seven hundred thirty-eight million, four hundred two thousand, two hundred eighty-one".