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A214840 Averages y of twin prime pairs that satisfy y = x^2 + x - 2. 1
4, 18, 108, 180, 270, 810, 4158, 4968, 5850, 7308, 10710, 13338, 17028, 26730, 32940, 38610, 70488, 72090, 102078, 117990, 122148, 128520, 132858, 153270, 228960, 231840, 240588, 246510, 249498, 296478, 326610, 372708, 391248, 417960, 429678, 449568, 453600 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The above equation is one of a family of twin prime average-generating quadratics y = x^2 + x - c, where c can be any even integer not of the form 6d + 4.

For f(x) = x^2 + x - c,  f(-x) = f(x-1).

If c = 0, the positive x that satisfy y = x^2 + x - c are A088485.

LINKS

Michael G. Kaarhus and Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 (first 334 terms from Kaarhus)

M. G. Kaarhus, A Family of Twin Prime Quads (PDF)

EXAMPLE

x =  2,  x =  4,  x = 10,  x = 13,  x = 16

x = 28,  x = 64,  x = 70,  x = 76,  x = 85

MATHEMATICA

s = {4}; Do[If[PrimeQ[n - 1] && PrimeQ[n + 1] && IntegerQ[Sqrt[9 + 4 n]], AppendTo[s, n]], {n, 18, 453600, 6}]; s (* Zak Seidov, Mar 21 2013 *)

PROG

(PARI) p=2; forprime(q=3, 1e6, if(q-p>2, p=q; next); n=sqrtint(y=(p+q)\2); if(n^2+n-2==y, print1(y", ")); p=q) \\ Charles R Greathouse IV, Mar 20 2013

(PARI) test(y)=if(isprime(y-1)&&isprime(y+1), print1(", "y))

print1(4); for(n=0, 100, test(18*n*(2*n+1)); test(18*(2*n^2+3*n+1))) \\ Charles R Greathouse IV, Mar 20 2013

CROSSREFS

Subsequence of A014574. Cf. A088485.

Sequence in context: A241841 A241842 A306003 * A060223 A144085 A003708

Adjacent sequences:  A214837 A214838 A214839 * A214841 A214842 A214843

KEYWORD

nonn

AUTHOR

Michael G. Kaarhus, Mar 07 2013

STATUS

approved

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Last modified May 29 03:06 EDT 2020. Contains 334696 sequences. (Running on oeis4.)