21516783787 has 2 divisors, whose sum is σ = 21516783788. Its totient is φ = 21516783786.

The previous prime is 21516783733. The next prime is 21516783793. The reversal of 21516783787 is 78738761512.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21516783787 is a prime.

It is a super-2 number, since 2×21516783787² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21516783727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10758391893 + 10758391894.

It is an arithmetic number, because the mean of its divisors is an integer number (10758391894).

Almost surely, 2^21516783787 is an apocalyptic number.

21516783787 is a deficient number, since it is larger than the sum of its proper divisors (1).

21516783787 is an equidigital number, since it uses as much as digits as its factorization.

21516783787 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3951360, while the sum is 55.

The spelling of 21516783787 in words is "twenty-one billion, five hundred sixteen million, seven hundred eighty-three thousand, seven hundred eighty-seven".