OFFSET
1,3
COMMENTS
It appears that this is also a triangle read by rows in which row n lists the first A000217(n) positive integers, n >= 1 (see example, second part). - Omar E. Pol, May 29 2012
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
1
1
2 3
1
2 3
4 5 6
1
2 3
4 5 6
7 8 9 10
1
2 3
4 5 6
7 8 9 10
11 12 13 14 15
From Omar E. Pol, May 29 2012: (Start)
Written as an irregular triangle the sequence begins:
1;
1, 2, 3;
1, 2, 3, 4, 5, 6;
1, 2, 3, 4, 5, 6, 7, 8, 9, 10;
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15;
Row n has length A000217(n). (End)
MAPLE
A000217 := proc(n) n*(n+1)/2 ; end : for t from 1 to 10 do for i from 1 to A000217(t) do printf("%d, ", i) ; od ; od ; # R. J. Mathar, May 18 2007
MATHEMATICA
Table[Range[(t(t+1))/2], {t, 10}]//Flatten (* Harvey P. Dale, Aug 06 2025 *)
PROG
(Python)
from math import comb
from sympy import integer_nthroot
def A124171(n): return n-comb((m:=integer_nthroot(6*n, 3)[0])+(n>comb(m+2, 3))+1, 3) # Chai Wah Wu, Nov 10 2024
CROSSREFS
KEYWORD
nonn,tabf,easy
AUTHOR
Colm Mulcahy, Dec 05 2006
EXTENSIONS
More terms from R. J. Mathar, May 18 2007
STATUS
approved
