27847

Properties

Appears in sequences

• Smallest prime with "n^2" as central digit(s).at n=28A038370
• A simple grammar.at n=7A052751
• a(n) = round(sqrt(a(n-2)^2 + a(n-1)^2)) with a(0) = 1 and a(1) = 2.at n=41A063827
• Numerator of Sum_{k=1..n} k/phi(k).at n=20A068885
• Shallow diagonal of triangular spiral in A051682.at n=39A081275
• Primes of the form 8*k^2 - 1.at n=26A090684
• "Rounded hypotenuses": a(n) = round(sqrt(a(n-1)^2 + a(n-2)^2)), a(1)=1, a(2)=3.at n=40A104804
• Primes p such that 2*p +/- 3 and 8*p +/- 3 are all primes.at n=14A106022
• Apocalypse primes: 10^665+a(n) has 666 decimal digits and is prime.at n=16A115983
• a(n) = (n^5 - 133*n^4 + 6729*n^3 - 158379*n^2 + 1720294*n - 6823316)/4.at n=14A121887
• A coefficients of characteristic polynomials of A_n Cartan matrices times their transposes: t(n,m,d)=If[ n == m, 2, If[n == m - 1 || n == m + 1, -1, 0]]. M(d)=t(n,m,d)*Transpose[t(n,m,d)].at n=40A158199
• Primes p of the form 4m+3 for which there are exactly as many primitive roots modulo p in the interval [0,p/2] as in the interval [p/2,p].at n=26A172490
• Smallest of 4 consecutive prime numbers that when represented as a simple continued fraction, generates prime numbers in the numerator and denominator, when reduced.at n=21A270884
• Primes of the form abs((1/4)*(n^5 - 133n^4 + 6729n^3 - 158379n^2 + 1720294n - 6823316)) in order of increasing nonnegative n.at n=14A272710
• Centered 21-gonal primes.at n=11A276261
• Integers which can be written in exactly three ways as sum of two distinct nonzero pentagonal numbers.at n=37A333013
• Numbers of the form (k^2 - 2) / 2 where k - 1 and k + 1 are both odd composite numbers.at n=33A339480
• Array read by antidiagonals: T(n,k) is the number of unlabeled oriented edge-rooted k-gonal 2-trees with n oriented polygons, n >= 0, k >= 2.at n=52A340814
• Primes in A343812.at n=23A343814
• Primes having only {2, 4, 7, 8} as digits.at n=42A386157