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%I #8 Jul 26 2013 04:47:10
%S 2,3,5,7,47,157,593,919,599,66593,46687,396937,467897,467899,6969647,
%T 16499897,367488959,598095997,2977884967,4977866987,2797986889,
%U 58888728979,58987779959,679585896989,4989996468997
%N Smallest prime p of the form prime(n)+k^2 such that sum of digits(p) = prime(n).
%C It is still an open problem if there exist infinitely many primes of form k^2 + d (d integer, no negative square).
%C For n<=4, k=0 suffices: e.g. prime(1)+0^2=2 = sum of digits(prime(1)), so a(n)=prime(n).
%e a(13) = 467897 because its digitsum is 41 which is the 13th prime, it is of the form prime(13)+k^2 with k=684, and it is the least such prime.
%o (PARI) sod(n) = {digs = digits(n, 10); return (sum(j=1, #digs, digs[j]));}
%o a(n) = {k = 0; p = prime(n); while (! (isprime(q=p+k^2) && (sod(q) == p)), k++); return (q);} \\ _Michel Marcus_, Jul 26 2013
%Y Cf. A000040, A172035, A176111, A176790
%K base,nonn
%O 1,1
%A Ulrich Krug (leuchtfeuer37(AT)gmx.de), May 23 2010
%E a(5) corrected and sequence extended by _D. S. McNeil_, May 25 2010