Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #15 Dec 26 2013 18:24:21
%S 3,13,41,113,331,443,613,1103,1013,1741,2543,3257,3691,4129,4889,6997,
%T 6491,8053,8443,12071,11681,12799,15439,18869,20759,21211,20807,27179,
%U 33791,28703,37339,39301,37813,53377,51853,54059,62801,60637,74149,72661,77687,62989,81749,79903,79589,109849,102547
%N a(n) = n-th smallest prime congruent to 1 modulo prime(n).
%H Zak Seidov and Charles R Greathouse IV, <a href="/A234387/b234387.txt">Table of n, a(n) for n = 1..10000</a> (first 1000 terms from Seidov)
%e a(3) = 41 because prime(3) = 5 and primes == 1 mod 5 are 11, 31, 41;
%e a(4) = 113 because prime(4) = 7 and primes == 1 mod 7 are 29, 43, 71, 113.
%t Reap[Sow[3];Do[c=0;q=Prime[n];p=1;While[c<n,p=p+2q;If[PrimeQ[p],c++]];Sow[p],{n,2,100}]][[2,1]]
%o (PARI) a(n)=if(n<2,return(3)); my(p=prime(n),q=2*p+1); while(n, if(isprime(q), n--); q+= 2*p); q-2*p \\ _Charles R Greathouse IV_, Dec 26 2013
%Y Cf. A035095, A234372.
%K nonn
%O 1,1
%A _Zak Seidov_, Dec 25 2013