21287689531 has 2 divisors, whose sum is σ = 21287689532. Its totient is φ = 21287689530.

The previous prime is 21287689519. The next prime is 21287689559. The reversal of 21287689531 is 13598678212.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21287689531 - 2⁷ = 21287689403 is a prime.

It is a super-2 number, since 2×21287689531² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21287609531) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10643844765 + 10643844766.

It is an arithmetic number, because the mean of its divisors is an integer number (10643844766).

Almost surely, 2^21287689531 is an apocalyptic number.

21287689531 is a deficient number, since it is larger than the sum of its proper divisors (1).

21287689531 is an equidigital number, since it uses as much as digits as its factorization.

21287689531 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1451520, while the sum is 52.

The spelling of 21287689531 in words is "twenty-one billion, two hundred eighty-seven million, six hundred eighty-nine thousand, five hundred thirty-one".