OFFSET
1,1
COMMENTS
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.
REFERENCES
David Wells, The Penguin Dictionary of Curious and Interesting Numbers.
MATHEMATICA
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[ # ]] &]
CROSSREFS
KEYWORD
nonn
AUTHOR
Alonso del Arte and Robert G. Wilson v, Aug 24 2004
STATUS
approved