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A141607 Nonprimes of the form n-(p(n+1)-p(n-2))/(p(n)-p(n-1)), where p(n)=n-th prime. 0


%S 0,1,4,6,8,9,10,12,15,20,21,22,24,25,26,27,33,35,36,44,45,48,50,51,57,

%T 60,62,63,68,69,72,74,75,82,84,85,90,93,98,105,110,111,115,121,122,

%U 126,129,134,135,136,138,142,143,144,145,147,148,158,165,166,169,170,172,174,176

%N Nonprimes of the form n-(p(n+1)-p(n-2))/(p(n)-p(n-1)), where p(n)=n-th prime.

%C Entries are not repeated and shown in natural order.

%e n=4: 4-(11-3)/(7-5)=0=a(1).

%e n=6: 6-(17-7)/(13-11)=1=a(2).

%e n=9: 9-(29-17)/(23-19)=6=a(4).

%e n=10: 10-(31-19)/(29-23)=8=a(5).

%e n=11: 11-(37-23)/(31-29)=4=a(3).

%t Select[PrimePi[#[[3]]]-(#[[4]]-#[[1]])/(#[[3]]-#[[2]])&/@ Partition[ Prime[ Range[200]],4,1],IntegerQ[#]&&!PrimeQ[#]&]//Union (* _Harvey P. Dale_, Jul 06 2017 *)

%Y Cf. A000040.

%K nonn

%O 1,3

%A _Juri-Stepan Gerasimov_, Sep 10 2008

%E Corrected and extended by _R. J. Mathar_, Sep 26 2008

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Last modified June 6 14:04 EDT 2020. Contains 334827 sequences. (Running on oeis4.)