21517783645 has 8 divisors (see below), whose sum is σ = 25830944856. Its totient is φ = 17207823936.

The previous prime is 21517783633. The next prime is 21517783669. The reversal of 21517783645 is 54638771512.

It can be written as a sum of positive squares in 4 ways, for example, as 3192476004 + 18325307641 = 56502^2 + 135371^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21517783645 - 2⁷ = 21517783517 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 785562 + ... + 812491.

It is an arithmetic number, because the mean of its divisors is an integer number (3228868107).

Almost surely, 2^21517783645 is an apocalyptic number.

It is an amenable number.

21517783645 is a deficient number, since it is larger than the sum of its proper divisors (4313161211).

21517783645 is a wasteful number, since it uses less digits than its factorization.

21517783645 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1600751.

The product of its digits is 1411200, while the sum is 49.

The spelling of 21517783645 in words is "twenty-one billion, five hundred seventeen million, seven hundred eighty-three thousand, six hundred forty-five".