21841

Properties

Appears in sequences

• Sextan primes: p = (x^6 + y^6)/(x^2 + y^2).at n=30A002647
• Primes of the form j^2 + (j+1)^2.at n=37A027862
• Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 98 ones.at n=21A031866
• Primes which, although they have correct parity, are not in the prime number maze.at n=31A065123
• Primes which can be expressed as sum of distinct powers of 4.at n=32A077718
• Third row of Pascal-(1,5,1) array A081580.at n=35A081589
• Expansion of (1+2x)^2/((1-x^2)(1-2x)).at n=12A085278
• Nontrivial Delannoy numbers that are primes.at n=39A101167
• Primes of the form 8*n^2 + 4*n + 1.at n=19A102130
• Smallest prime of the form 2n*(2n+2)*(2n+4)*...*(2n+2k) + 1 where k is a nonnegative integer.at n=12A110336
• Primes p such that their cubes are pandigital.at n=14A124629
• Centered square numbers that are prime powers of the form (4n+1)^k.at n=39A133322
• Primes A080478(n)^2 + A080478(n+1)^2.at n=17A139361
• Number of n X n binary arrays symmetric under 90 degree rotation with all ones connected only in a 0010-1010-1111 pattern in any orientation.at n=14A146781
• Primes of the form (4*n^2-8*n-9)/3.at n=33A154616
• Hypotenuse C of primitive Pythagorean triangles such that perimeters are Averages of twin prime pairs, q=p+1, a=q^2-p^2, c=q^2+p^2, b=2*p*q, s=a+b+c, s-+1 are primes.at n=13A155175
• Primes in A155175.at n=7A155185
• Primes that are the difference between a fourth power and a positive cube.at n=33A161735
• Twin prime pairs p, p+2 such that p+(p+2)+1 and p*(p+2)+1 are both square.at n=21A166564
• Primes that become squares when prefixed with a 2.at n=15A167735