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%I #3 Mar 31 2012 13:21:55
%S 1,0,1,0,1,1,0,0,0,1,1,1,0,0,0,0,1,3,6,1,5,1,0,1,0,1,1,6,1,1,5,0,4,2,
%T 4,6,7,1,6,21,1,2,2,1,1,4,2,3,3,1,2,2,7,1,7,5,2,1,5,3,1,2,0,2,2,2,1,1,
%U 2,1,4,3,3,2,2,1,5,5,34,1,2,4,1,3,7,1,2,4,1,5,3,2,7,4,2,10,1,2
%N sigma(sigma(..(sigma(n)+1)..)) is prime, or 0 if no prime is reached.
%e a(18)=3 as sigma(18)+1=40, sigma(40)+1=91, sigma(91)+1=113, which is prime
%o (PARI) sr(m,c)=if (c>0,m=sigma(m)+1; c--; sr(m,c),m) for (n=1,100, x=1; while (!isprime(sr(n,x)) && x<200, x++); if (x==200,x=0); print1(x","))
%K nonn
%O 1,18
%A _Jon Perry_, Jan 09 2003
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