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A154670 Averages of twin prime pairs k such that k*2 and k/2 are squares. 10
18, 72, 882, 1152, 2592, 3528, 4050, 15138, 20808, 34848, 46818, 69192, 83232, 103968, 112338, 149058, 176418, 180000, 206082, 281250, 362952, 388962, 438048, 472392, 478242, 538722, 649800, 734472, 808992, 960498, 1080450, 1143072 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = 18*A037073(n)^2. - M. F. Hasler, Jan 15 2009

EXAMPLE

18/2 = 9 = 3^2, 18*2 = 36 = 6^2.

MATHEMATICA

lst={}; Do[If[PrimeQ[n-1]&&PrimeQ[n+1], s=Sqrt[n*2]; If[Floor[s]==s, AppendTo[lst, n]]], {n, 6, 10!, 6}]; lst...and/or... lst={}; Do[If[PrimeQ[n-1]&&PrimeQ[n+1], s=Sqrt[n/2]; If[Floor[s]==s, AppendTo[lst, n]]], {n, 6, 10!, 6}]; lst

PROG

(PARI) for(i=1, 999, isprime(18*i^2+1) && isprime(18*i^2-1) && print1(18*i^2", ")) \\ M. F. Hasler, Jan 15 2009

CROSSREFS

Cf. A037073.

Sequence in context: A052619 A110753 A174085 * A041626 A039608 A211619

Adjacent sequences:  A154667 A154668 A154669 * A154671 A154672 A154673

KEYWORD

nonn

AUTHOR

Vladimir Joseph Stephan Orlovsky, Jan 13 2009

STATUS

approved

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Last modified July 3 18:46 EDT 2020. Contains 335418 sequences. (Running on oeis4.)