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Smallest number such that a(n) + T(n) is a prime, where T(n) is the n-th triangular number.
4

%I #6 Dec 05 2013 19:55:38

%S 1,0,1,1,2,2,1,1,2,4,1,1,6,2,7,1,4,2,1,1,2,4,1,7,6,2,1,3,4,2,3,13,2,4,

%T 1,7,6,2,7,1,2,4,1,1,4,6,1,5,4,2,1,3,2,2,3,1,4,10,7,1,10,20,1,1,8,2,3,

%U 1,2,18,1,5,6,2,1,1,8,2,3,11,2,4,5,1,4,20,5,1,2,4,15,5,2,16,1,1,6,10,1

%N Smallest number such that a(n) + T(n) is a prime, where T(n) is the n-th triangular number.

%C 0 occurs only once in this sequence.

%H Harvey P. Dale, <a href="/A075402/b075402.txt">Table of n, a(n) for n = 1..1000</a>

%t If[PrimeQ[#],#,NextPrime[#]]-#&/@Accumulate[Range[100]] (* _Harvey P. Dale_, Nov 21 2012 *)

%o (PARI) for(n=1,100,a=n*(n+1)/2:print1(nextprime(a)-a","))

%Y Cf. A075403.

%K nonn

%O 1,5

%A _Amarnath Murthy_, Sep 23 2002

%E Corrected and extended by _Ralf Stephan_, Mar 19 2003