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(prime(n)*(prime(n+1)-1) + (prime(n)-1)*prime(n+1)) / 2.
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%I #10 Nov 10 2013 07:19:46

%S 11,29,68,131,206,305,416,641,869,1113,1478,1721,1976,2441,3071,3539,

%T 4023,4688,5111,5691,6476,7301,8540,9698,10301,10916,11555,12206,

%U 14231,16508,17813,18905,20567,22349,23553,25431,27056,28721,30791,32219

%N (prime(n)*(prime(n+1)-1) + (prime(n)-1)*prime(n+1)) / 2.

%C See A099911 for primes; A099910(n)=A001222(a(n)).

%H Harvey P. Dale, <a href="/A099909/b099909.txt">Table of n, a(n) for n = 2..1000</a>

%t pn[{a_,b_}]:=(a(b-1)+b(a-1))/2; pn/@Partition[Prime[Range[2,50]],2,1] (* _Harvey P. Dale_, Nov 08 2013 *)

%o (Haskell)

%o a099909 n = a099909_list !! (n-2)

%o a099909_list = map (flip div 2) $ tail $ zipWith (+)

%o (zipWith (*) a000040_list $ map (subtract 1) $ tail a000040_list)

%o (zipWith (*) (map (subtract 1) a000040_list) $ tail a000040_list)

%o -- _Reinhard Zumkeller_, Nov 10 2013

%K nonn

%O 2,1

%A _Reinhard Zumkeller_, Oct 29 2004