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%I #5 Mar 31 2012 20:30:55
%S 497,1771,2279,3161,3487,5149,5357,5993,6439,8129,9451,9731,11477,
%T 15049,16469,18337,19901,25879,26333,28681,29159,34717,40187,43069,
%U 48517,50401,54947,60379,61073,62479,67529,69749,72011,73537,79001,88829
%N Counterexamples to the conjecture that an even, prime-indexed triangular plus 1 equals a prime or that an odd, prime-indexed triangular minus 2 equals a prime.
%C In the entry for 496, Wells remarks that it is the smallest counterexample to the conjecture that an even, prime-indexed triangular plus 1 equals a prime, since 497 is not prime.
%D David Wells, The Penguin Dictionary of Curious and Interesting Numbers.
%t tri[n_] := n(n + 1)/2; tp = Table[ tri[ Prime[n]], {n, 2, 85}]; f[n_] := If[ OddQ[n], n - 2, n + 1]; Select[f /@ tp, Not[ PrimeQ[ # ]] &]
%Y Cf. A096333.
%K nonn
%O 1,1
%A _Alonso del Arte_ and _Robert G. Wilson v_, Aug 24 2004