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A152950 a(n) = 3 + n*(n-1)/2. 10
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

Table of n, a(n) for n=1..54.

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 xrange(1, 55)] # Zerinvary Lajos, Mar 12 2009

(PARI) a(n)=3+n*(n-1)/2 \\ Charles R Greathouse IV, Oct 07 2015

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

AUTHOR

Vladimir Joseph Stephan Orlovsky, Dec 15 2008

STATUS

approved

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Last modified February 16 14:47 EST 2019. Contains 320163 sequences. (Running on oeis4.)