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%I #9 Dec 07 2012 19:53:14
%S 2,0,3,35,71,1151,1079,4199,11879,7559,32759,30239,75599,171359,
%T 241919,251999,262079,393119,604799,665279,1572479,1834559,2827439,
%U 2570399,2358719,7862399,7814015,5405399,6683039,18017999,20180159,8648639,17992799,17297279
%N The least number having n representations as p*q - p - q for primes p <= q.
%C a(72) > 2^32. - _Donovan Johnson_, Dec 07 2012
%H Donovan Johnson, <a href="/A218862/b218862.txt">Table of n, a(n) for n = 0..71</a>
%e The values of a(n) and (p,q) for n = 1 to 6:
%e 0 is (2,2).
%e 3 is (2,5), (3,3).
%e 35 is (2,37), (3,19), (7,7).
%e 71 is (2,73), (3,37), (5,19), (7,13).
%e 1151 is (2,1153), (3,577), (7,193), (13,97), (17,73).
%e 1079 is (3,541), (5,271), (7,181), (11,109), (19,61), (31,37).
%t nn = 10000; ps = Prime[Range[PrimePi[nn + 1]]]; t = Table[0, {nn}]; Do[n = p*q - p - q; If[p <= q && 0 < n <= nn, t[[n]]++], {p, ps}, {q, ps}]; t = Join[{1}, t]; u = Union[t]; c = Complement[Range[Max[u]], u]; If[c == {}, mx = u[[-1]], mx = c[[-1]] - 1]; Table[Position[t, n, 1, 1][[1, 1]] - 1, {n, 0, mx}]
%Y Cf. A157187.
%K nonn
%O 0,1
%A _T. D. Noe_, Dec 06 2012