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

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A209978 a(n) = A196227(n)/2. 9
0, 0, 1, 4, 7, 14, 17, 28, 35, 46, 53, 72, 79, 102, 113, 128, 143, 174, 185, 220, 235, 258, 277, 320, 335, 374, 397, 432, 455, 510, 525, 584, 615, 654, 685, 732, 755, 826, 861, 908, 939, 1018, 1041, 1124, 1163, 1210, 1253, 1344, 1375, 1458, 1497 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

See A210000 for a guide to related sequences.

LINKS

Table of n, a(n) for n=0..50.

MAPLE

a:= proc(n) option remember; `if`(n<2, 0,

a(n-1)-1 + 2*numtheory[phi](n))

end:

seq(a(n), n=0..60); # Alois P. Heinz, May 05 2020

MATHEMATICA

a = 1; b = n; z1 = 50;

t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]]

c[n_, k_] := c[n, k] = Count[t[n], k]

Table[c[n, 0], {n, 0, z1}] (* A134506 *)

Table[c[n, 1], {n, 0, z1}] (* A196227 *)

%/2 (* A209978 *)

Table[2 c[n, 1], {n, 0, z1}](* A209979 *)

Table[c[n, 2], {n, 0, z1}] (* A197168 *)

%/2 (* A209980 *)

Table[c[n, 3], {n, 0, z1}] (* A210001 *)

Table[c[n, 4], {n, 0, z1}] (* A210002 *)

Table[c[n, 5], {n, 0, z1}] (* A210027 *)

CROSSREFS

Cf. A196227, A210000.

Sequence in context: A310910 A310911 A255649 * A294016 A344533 A310912

Adjacent sequences: A209975 A209976 A209977 * A209979 A209980 A209981

KEYWORD

nonn

AUTHOR

Clark Kimberling, Mar 16 2012

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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 5 20:57 EST 2023. Contains 360087 sequences. (Running on oeis4.)