21621745405 has 16 divisors (see below), whose sum is σ = 27952328880. Its totient is φ = 15960895488.

The previous prime is 21621745361. The next prime is 21621745501. The reversal of 21621745405 is 50454712612.

It can be written as a sum of positive squares in 8 ways, for example, as 1465128729 + 20156616676 = 38277^2 + 141974^2 .

It is a cyclic number.

It is not a de Polignac number, because 21621745405 - 2²³ = 21613356797 is a prime.

It is a super-2 number, since 2×21621745405² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 118531 + ... + 239359.

It is an arithmetic number, because the mean of its divisors is an integer number (1747020555).

Almost surely, 2^21621745405 is an apocalyptic number.

It is an amenable number.

21621745405 is a deficient number, since it is larger than the sum of its proper divisors (6330583475).

21621745405 is a wasteful number, since it uses less digits than its factorization.

21621745405 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 123600.

The product of its (nonzero) digits is 67200, while the sum is 37.

The spelling of 21621745405 in words is "twenty-one billion, six hundred twenty-one million, seven hundred forty-five thousand, four hundred five".