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 A125602 Centered triangular numbers that are prime. 8
 19, 31, 109, 199, 409, 571, 631, 829, 1489, 1999, 2341, 2971, 3529, 4621, 4789, 7039, 7669, 8779, 9721, 10459, 10711, 13681, 14851, 16069, 16381, 17659, 20011, 20359, 23251, 25939, 27541, 29191, 29611, 31321, 34429, 36739, 40099, 40591, 42589 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Prime terms in A005448, or primes of the form 3n(n-1)/2 + 1. Primes that are the sum of 3 consecutive triangular numbers. - Vicente Izquierdo Gomez, Nov 03 2015 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 MAPLE select(isprime, [seq(3*n*(n-1)/2+1, n=1..1000)]); # Robert Israel, Nov 03 2015 MATHEMATICA lst={}; Do[If[PrimeQ[p=3n(n-1)/2+1], (*Print[p]; *)AppendTo[lst, p]], {n, 10^3}]; lst (* Vladimir Joseph Stephan Orlovsky, Aug 21 2008 *) PROG (MAGMA) [a: n in [0..200] | IsPrime(a) where a is  (3*n^2 - 3*n + 2) div 2]; // Vincenzo Librandi, Mar 22 2013 (PARI) is(n)=n%6==1 && ispolygonal((n-1)/3, 3) && isprime(n) \\ Charles R Greathouse IV, Nov 03 2015 CROSSREFS Cf. A005448, A125603. Sequence in context: A243450 A237418 A240126 * A139847 A087764 A146691 Adjacent sequences:  A125599 A125600 A125601 * A125603 A125604 A125605 KEYWORD nonn,easy AUTHOR Zak Seidov, Nov 27 2006 STATUS approved

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Last modified November 16 09:17 EST 2018. Contains 317268 sequences. (Running on oeis4.)