This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A202391 Indices of the smallest of four consecutive triangular numbers summing up to a square. 6

%I

%S 5,39,237,1391,8117,47319,275805,1607519,9369317,54608391,318281037,

%T 1855077839,10812186005,63018038199,367296043197,2140758220991,

%U 12477253282757,72722761475559,423859315570605,2470433131948079

%N Indices of the smallest of four consecutive triangular numbers summing up to a square.

%C Positive integers n such that A000217(n) + A000217(n + 1) + A000217(n + 2) + A000217(n + 3) is a square (=A075870(n+1)^2).

%H <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (7,-7,1).

%F a(n) = A002315(n) - 2.

%F G.f. x*(1+x)*(x-5) / ( (x-1)*(1-6*x+x^2) ). - _R. J. Mathar_, Dec 19 2011

%F a(n+2) = 6*a(n+1) - a(n) + 8; a(n+3) = 7*a(n+2) - 7*a(n+1) + a(n); a(n+1) = (-4 + (7 + 5*r)*(3 + 2*r)^n + (7 - 5*r)*(3 - 2*r)^n)/2 where r = sqrt(2). - _Paul Weisenhorn_, Jan 13 2013

%Y Cf. A176541, A176542, A165517, A116476, A075870

%K nonn

%O 1,1

%A _Max Alekseyev_, Dec 18 2011

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 11 02:13 EST 2019. Contains 329910 sequences. (Running on oeis4.)