21781741 has 4 divisors (see below), whose sum is σ = 21885184. Its totient is φ = 21678300.

The previous prime is 21781723. The next prime is 21781751. The reversal of 21781741 is 14718712.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21781741 - 2¹⁵ = 21748973 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21781751) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 51405 + ... + 51826.

It is an arithmetic number, because the mean of its divisors is an integer number (5471296).

Almost surely, 2^21781741 is an apocalyptic number.

It is an amenable number.

21781741 is a deficient number, since it is larger than the sum of its proper divisors (103443).

21781741 is a wasteful number, since it uses less digits than its factorization.

21781741 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 103442.

The product of its digits is 3136, while the sum is 31.

The square root of 21781741 is about 4667.0912783017. The cubic root of 21781741 is about 279.2742300980.

It can be divided in two parts, 21781 and 741, that multiplied together give a triangular number (16139721 = T₅₆₈₁).

The spelling of 21781741 in words is "twenty-one million, seven hundred eighty-one thousand, seven hundred forty-one".