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%I #17 May 13 2013 01:49:30
%S 0,1,6,9,15,14,21,24,22,43,38,50,54,43,61,62,74,66,79,81,87,94,93,99,
%T 101,101,110,114,119,123,129,136,160,150,184,158,178,196,171,176,180,
%U 190,201,202,222,221,230,252,242,244,251,235,261,262
%N a(n) is the number of odd primes p < prime(n)^2 such that prime(n)# - p is prime.
%C a(n) is not so far from prime(n).
%H Pierre CAMI, <a href="/A185398/b185398.txt">Table of n, a(n) for n = 1..176</a>
%e prime(1)#=2 , a(n)=0 ( no solution )
%e prime(2)#=6 , 6-3=3 prime , a(1)=1
%e prime(3)#=30, 30-7=23,30-11=19,30-13=17,30-17=13,30-19=11,30-23=7
%e so a(3)=6
%o (PFGW Scriptify) SCRIPT
%o DIM nn,1
%o DIM kk
%o DIM cc
%o DIM dd
%o DIMS tt
%o DIMS ss
%o OPENFILEOUT myout,res
%o LABEL loopn
%o SET nn,nn+1
%o SET kk,nn
%o SET cc,0
%o SET dd,0
%o LABEL loopk
%o SET kk,kk+1
%o IF p(kk)>p(nn)^2 THEN GOTO a
%o SETS tt,%d,%d,%d\,;nn;p(nn);-p(kk)
%o PRP p(nn)#-p(kk),tt
%o IF ISPRIME THEN SET cc,cc+1
%o IF ISPRP THEN SET cc,cc+1
%o SETS tt,%d,%d,%d\,;nn;p(nn);p(kk)
%o PRP p(nn)#+p(kk),tt
%o IF ISPRIME THEN SET dd,dd+1
%o IF ISPRP THEN SET dd,dd+1
%o GOTO loopk
%o LABEL a
%o SETS ss,%d,%d,%d\,;nn;cc;dd
%o WRITE myout,ss
%o GOTO loopn
%o (PARI) a(n)=my(P=prod(k=1,n,prime(k)),s=0); forprime(p=2,prime(n)^2, s+=ispseudoprime(P-p));s
%Y Cf. A186413.
%K nonn
%O 1,3
%A _Pierre CAMI_, Feb 21 2011
%E Edited by _Charles R Greathouse IV_, Feb 21 2011
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