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 A152950 a(n) = 3 + n*(n-1)/2. 12
 3, 4, 6, 9, 13, 18, 24, 31, 39, 48, 58, 69, 81, 94, 108, 123, 139, 156, 174, 193, 213, 234, 256, 279, 303, 328, 354, 381, 409, 438, 468, 499, 531, 564, 598, 633, 669, 706, 744, 783, 823, 864, 906, 949, 993, 1038, 1084, 1131, 1179, 1228, 1278, 1329, 1381, 1434 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(1)=3; then add 1 to the first number, then 2,3,4... and so on. Numbers m such that 8m-23 is a square. - Bruce J. Nicholson, Jul 25 2017 LINKS Michael De Vlieger, Table of n, a(n) for n = 1..10000 Ângela Mestre, José Agapito, Square Matrices Generated by Sequences of Riordan Arrays, J. Int. Seq., Vol. 22 (2019), Article 19.8.4. Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA a(n) = A152949(n+1) = 3+A000217(n-1). - R. J. Mathar, Jan 03 2009 a(n) = 3+C(n,2), n>=1. - Zerinvary Lajos, Mar 12 2009 a(n) = a(n-1)+n-1 (with a(1)=3). - Vincenzo Librandi, Nov 27 2010 MAPLE A152950:=n->3 + n*(n-1)/2; seq(A152950(n), n=1..100); # Wesley Ivan Hurt, Jan 28 2014 MATHEMATICA s=3; lst={3}; Do[s+=n; AppendTo[lst, s], {n, 1, 5!}]; lst Table[3 + n*(n-1)/2, {n, 100}] (* Wesley Ivan Hurt, Jan 28 2014 *) PROG (Sage) [3+binomial(n, 2) for n in range(1, 55)] # Zerinvary Lajos, Mar 12 2009 (PARI) a(n)=3+n*(n-1)/2 \\ Charles R Greathouse IV, Oct 07 2015 (MAGMA) [3+n*(n-1)/2 : n in [1..50]]; // Wesley Ivan Hurt, Mar 25 2020 CROSSREFS Cf. A000217, A152947, A000124, A152948, A152949. Sequence in context: A289117 A167928 A090867 * A005626 A227561 A030712 Adjacent sequences:  A152947 A152948 A152949 * A152951 A152952 A152953 KEYWORD nonn,easy,changed AUTHOR Vladimir Joseph Stephan Orlovsky, Dec 15 2008 STATUS approved

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Last modified April 8 00:29 EDT 2020. Contains 333311 sequences. (Running on oeis4.)