21613

Properties

Appears in sequences

• Primes of form k^2 + 4.at n=27A005473
• Primes p for which the period of reciprocal 1/p is (p-1)/12.at n=26A056217
• Primes with 4 distinct digits that remain prime (no leading zeros allowed) after deleting all occurrences of its digits d.at n=5A057880
• Primes such that the sum of their digits and the sum of the reciprocals of their digits is also prime.at n=12A064779
• Greater of twin primes of the form x^2+2, x^2+4.at n=7A085554
• Primes p of the form x^2+4, such that either p-2 or p+2 is prime.at n=10A085555
• Primes of the form n^2 + 4n + 8.at n=26A098062
• Primes p containing the string "13" and sum of digits sod(p) = 13.at n=22A175017
• Sequence of primes separated by [sequence of prime] elements. 2, [find 2nd prime after 2 = ] 5, [find 3rd prime after 5 =] 13, [find 5th prime after 13 =] 61, ..., etc.at n=36A180302
• Primes of the form floor(k^sqrt(Pi)).at n=42A180452
• Number of nX6 binary arrays with each 1 adjacent to exactly one 0 vertically and one 0 horizontally.at n=6A183348
• Number of nX7 binary arrays with each 1 adjacent to exactly one 0 vertically and one 0 horizontally.at n=5A183349
• Primes of the form 9n^2 + 4.at n=9A201706
• n-th prime p such that (p+n)^2+n is prime but (p+j)^2+j is not prime for all 0<j<n.at n=15A238663
• Primes whose sum of reciprocal of digits is a prime.at n=14A266815
• Number of n X 1 0..2 arrays with every repeated value in every row unequal to the previous repeated value, and in every column equal to the previous repeated value, and new values introduced in row-major sequential order.at n=11A267905
• Let F(g,p) be the frequency of g up to prime nextprime(p+1). Primes p such that F(2,p) = F(4,p) and g = 2 or 4.at n=41A274122
• Numbers n such that (n-2,n) are twin primes, and (n,n+2) are twin lucky numbers.at n=42A289123
• Numbers k such that phi(k) > phi(k+1) > phi(k+2) > phi(k+3) where phi is the Euler totient function (A000010).at n=36A326817
• Prime numbers p such that the product of their prime digits is equal to the product of their nonprime digits, where p has at least one prime digit.at n=17A369877