The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A333818 G.f.: Sum_{k>=1} x^(k*(3*k - 2)) / (1 - x^(6*k)). 6
 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 1, 1, 1, 0, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1 COMMENTS Number of ways to write n as the difference of two octagonal numbers. a(n) = 2 if n = 133, 175, 176, 217, 224, 259, 272, 280, 301, 320, 343, 368, 385, 400, ... a(n) = 3 if n = 560, 637, 896, 935, ... a(n) = 4 if n = 1729, 2240, 2275, ... - R. J. Mathar, Oct 08 2020 [modified by Ilya Gutkovskiy, Oct 09 2020] LINKS FORMULA G.f.: Sum_{i>=0} Sum_{j>=i} Product_{k=i..j} x^(6*k + 1). EXAMPLE a(1729) = 4 with representations 1729 = 1825-96 = 2465-736 = 5985-4256 = 249985-248256. - R. J. Mathar, Oct 08 2020 MAPLE A333818 := proc(n)     local a, hi, hiO, lo, loO;     a := 0 ;     for hi from 1 do         hiO := A000567(hi) ;         for lo from hi-1 to 1 by -1 do             loO := A000567(lo) ;             if lo = hi-1 and hiO-loO > n then                 return a;             end if;             if hiO-loO = n then                 a := a+1 ;             elif hiO-loO > n then                 break;             end if ;         end do:     end do: end proc: seq( A333818(n), n=1..300) ; # R. J. Mathar, Oct 08 2020 MATHEMATICA nmax = 95; CoefficientList[Series[Sum[x^(k (3 k - 2))/(1 - x^(6 k)), {k, 1, nmax}], {x, 0, nmax}], x] // Rest CROSSREFS Cf. A000567, A001227, A034178, A333815, A333816, A333817, A334037. Sequence in context: A266243 A266608 A066288 * A111412 A080111 A204545 Adjacent sequences:  A333815 A333816 A333817 * A333819 A333820 A333821 KEYWORD nonn AUTHOR Ilya Gutkovskiy, Apr 06 2020 STATUS approved

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 January 27 14:59 EST 2022. Contains 350607 sequences. (Running on oeis4.)