21661

Properties

Appears in sequences

• Sextan primes: p = (x^6 + y^6)/(x^2 + y^2).at n=29A002647
• Primes that divide at least one term of Sylvester's sequence s = A000058: s(n+1) = s(n)^2 - s(n) + 1, s(0) = 2.at n=37A007996
• Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 84 ones.at n=22A031852
• Odd k for which k+2^m is composite for all m < k.at n=13A033919
• Primes such that the sum of the factorials of the digits is a perfect square.at n=38A052279
• Primes p such that p-12, p and p+12 are consecutive primes.at n=21A053072
• Primes which can be expressed as concatenation of powers of 6 and 0's.at n=25A066597
• Class 6+ primes.at n=27A081634
• Number triangle read by rows: T(n,k) = Sum_{j=0..n-k} C(n+j,j+k)*C(n-j,k).at n=39A117207
• Smallest prime p such that p divides m^(m+1)+1, where m = (p-2n-1)/(2n).at n=37A123571
• Primes p such that p+-2 and p+-3 are not squarefree.at n=10A153214
• a(n) = 60*n^2 + 1.at n=19A158673
• Expansion of x*(1+2*x+8*x^2+4*x^3+3*x^4) / ( (1+x)^2*(x-1)^4 ).at n=30A178947
• Number of (n+2) X 4 0..3 arrays with every 3 X 3 subblock commuting with each horizontal and vertical neighbor 3 X 3 subblock.at n=6A186874
• Number of (n+2)X9 0..3 arrays with every 3X3 subblock commuting with each horizontal and vertical neighbor 3X3 subblock.at n=1A186879
• T(n,k)=Number of (n+2)X(k+2) 0..3 arrays with every 3X3 subblock commuting with each horizontal and vertical neighbor 3X3 subblock.at n=29A186881
• T(n,k)=Number of (n+2)X(k+2) 0..3 arrays with every 3X3 subblock commuting with each horizontal and vertical neighbor 3X3 subblock.at n=34A186881
• Primes of the form T(k) + S(k) + 1 where T(k) is the k-th triangular number and S(k) is the k-th square number.at n=28A229080
• Lesser of consecutive primes whose sum is a palindromic number.at n=27A242386
• Number of (n+2) X (5+2) 0..4 arrays with every consecutive three elements in every row and diagonal having exactly two distinct values, and in every column and antidiagonal not having exactly two distinct values, and new values 0 upwards introduced in row major order.at n=8A252958