21481

Properties

Appears in sequences

• Primes p such that p, p+6, p+12, p+18 are all primes.at n=36A023271
• Primes that are palindromic in base 5.at n=29A029973
• Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 84 ones.at n=21A031852
• Third term of strong prime sextets: p(m-1)-p(m-2) > p(m)-p(m-1) > p(m+1)-p(m) > p(m+2)-p(m+1) > p(m+3)-p(m+2).at n=4A054815
• Initial term in sequence of four consecutive primes separated by 3 consecutive differences each <=6 (i.e., when d=2,4 or 6) and forming d-pattern=[6, 4,2]; short d-string notation of pattern = [642].at n=26A078855
• Primes p such that the differences between the 5 consecutive primes starting with p are (6,4,2,6).at n=4A078962
• Primes p such that each of the numbers p^k for k=1..5 has exactly two 1s in its decimal representation.at n=3A175964
• Primes of the form x^2 + 5*y^2, where x and y=x+1 are consecutive natural numbers.at n=17A176608
• Numbers k such that sum of digits of k = sum of digits of anti-divisors of k.at n=13A213239
• Primes p such that p^4 - p +/- 1 are twin primes.at n=17A236952
• Numbers for which the cube of the sum of the digits is equal to the square of the product of their digits.at n=31A241846
• Numbers n such that the digit sum of Fibonacci(n) is equal to the digit sum of Lucas(n).at n=40A244923
• a(n) is the smallest k such that prime(k+i) (mod 6) takes successively the values 5, 5, ... for i = 0, 1, ..., n-1.at n=7A247967
• a(n) = 137*n^2 - 4043*n + 27277.at n=28A267706
• Hyperartiads.at n=19A270798
• Primes of the form k!6-24, where k!6 is the sextuple factorial number (A085158).at n=4A289733
• Number of faces in the n-polygon diagonal intersection graph.at n=26A301748
• Prime numbers congruent to 49 or 121 modulo 240 representable by x^2 + 150*y^2.at n=35A325089
• a(n) = Sum_{k=1..n+1} |A341287(n,k)|.at n=9A341323
• Primes that begin a run of consecutive primes in A375564.at n=13A376193