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A215684 Let  p=prime=a(n); then a(n+1) = smallest prime q>p such that 2p+q and 2q+p are both primes. 2
3, 5, 7, 17, 67, 107, 277, 353, 487, 557, 787, 797, 853, 983, 1033, 1163, 1597, 1637, 1657, 1697, 1867, 1913, 2347, 2543, 2833, 2897, 2953, 2957, 3343, 3413, 3607, 3623, 3643, 3863, 3907, 4013, 4447, 4583, 4987, 5087, 5113, 5507, 6277, 6653, 7027, 7433, 7603 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Zak Seidov, Table of n, a(n) for n = 1..1000

EXAMPLE

2*3+5=11 and 2*5+3=13 are both prime, so a(2) = 5.

2*7+17=31 and 2*17+7=41 are both prime, so a(4) = 17.

MATHEMATICA

a=3; s={a}; m=100; Do[n1=PrimePi[a]+1; Do[b=Prime[n]; If[PrimeQ[2*a+b]&&PrimeQ[2*b+a], AppendTo[s, b]; a=b; Break[]], {n, n1, n1+100000}], {m-1}]; s

spq[n_]:=Module[{p=NextPrime[n]}, While[!PrimeQ[2n+p]||!PrimeQ[2p+n], p=NextPrime[p]]; p]; NestList[spq, 3, 50] (* Harvey P. Dale, Apr 06 2019 *)

CROSSREFS

Cf. A181848.

Sequence in context: A038893 A191064 A075227 * A229132 A270779 A248796

Adjacent sequences:  A215681 A215682 A215683 * A215685 A215686 A215687

KEYWORD

nonn

AUTHOR

Zak Seidov, Aug 20 2012

STATUS

approved

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Last modified September 18 10:31 EDT 2020. Contains 337166 sequences. (Running on oeis4.)