The OEIS mourns the passing of Jim Simons and is grateful to the Simons Foundation for its support of research in many branches of science, including the OEIS.
The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A113502 A number n is included if at least one of its divisors > 1 is a triangular number (i.e., is of the form m(m+1)/2, m >= 2). 8
 3, 6, 9, 10, 12, 15, 18, 20, 21, 24, 27, 28, 30, 33, 36, 39, 40, 42, 45, 48, 50, 51, 54, 55, 56, 57, 60, 63, 66, 69, 70, 72, 75, 78, 80, 81, 84, 87, 90, 91, 93, 96, 99, 100, 102, 105, 108, 110, 111, 112, 114, 117, 120, 123, 126, 129, 130, 132, 135, 136, 138, 140, 141 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A number n is in the sequence iff it is not a "triangle-free" positive integer. Multiples of A226863. - Charles R Greathouse IV, Jul 29 2016 LINKS Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 FORMULA a(n) = A088723(n)/2. - Ray Chandler, May 29 2008 EXAMPLE 12 is included because its divisors are 1, 2, 3, 4, 6 and 12, two of which (3 and 6) are triangular numbers > 1. MATHEMATICA v={}; Do[If[b=Select[Divisors[n], #>1 && IntegerQ[(1+8#)^(1/2)]&]; b!={}, AppendTo[v, n]], {n, 200}]; v (* Farideh Firoozbakht, Jan 12 2006 *) Select[Range[200], AnyTrue[Rest[Divisors[#]], OddQ[Sqrt[8#+1]]&]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Dec 13 2017 *) PROG (PARI) is(n)=fordiv(n, d, if(ispolygonal(d, 3) && d>1, return(1))); 0 \\ Charles R Greathouse IV, Jul 29 2016 CROSSREFS Cf. A112886, A000217, A013929, A226863. Sequence in context: A055632 A133006 A055264 * A229307 A356453 A061904 Adjacent sequences: A113499 A113500 A113501 * A113503 A113504 A113505 KEYWORD nonn AUTHOR Leroy Quet, Jan 10 2006 EXTENSIONS More terms from Farideh Firoozbakht, Jan 12 2006 STATUS approved

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

Last modified May 29 12:05 EDT 2024. Contains 372940 sequences. (Running on oeis4.)