|
|
A115904
|
|
Numbers k such that k + sigma(k) is a triangular number.
|
|
3
|
|
|
7, 10, 66, 136, 145, 196, 198, 234, 270, 438, 495, 528, 592, 606, 855, 910, 1045, 1158, 1428, 2208, 2718, 2922, 3016, 3663, 3808, 3916, 4506, 4975, 5043, 5136, 5598, 6366, 6600, 7080, 7498, 7821, 8172, 8200, 8217, 8814, 9318, 9730, 9738
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
LINKS
|
|
|
EXAMPLE
|
234 + sigma(234) = 780 = T(39).
|
|
MATHEMATICA
|
trnoQ[n_]:=IntegerQ[(Sqrt[1+8n]-1)/2]; Select[Range[10000], trnoQ[#+ DivisorSigma[ 1, #]]&] (* Harvey P. Dale, Apr 26 2014 *)
|
|
PROG
|
(PARI) isok(n) = ispolygonal(n + sigma(n), 3); \\ Michel Marcus, Jan 25 2014
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|