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A067520
Triangular numbers whose index is a multiple of the sum of their digits.
2
1, 10, 21, 45, 55, 120, 171, 300, 465, 666, 820, 1035, 1485, 1830, 2016, 2211, 2628, 2850, 2926, 3321, 4095, 5050, 5565, 5886, 7260, 8001, 8911, 10011, 10440, 13203, 14196, 16290, 17955, 18145, 18528, 19701, 20910, 22155, 23436, 24310, 29646
OFFSET
1,2
LINKS
EXAMPLE
T(30) = 465 and 30 = 2*(4+6+5).
MAPLE
f:= proc(n) local t;
t:= n*(n+1)/2;
if n mod convert(convert(t, base, 10), `+`) = 0 then return t fi
end proc:
map(f, [$1..300]); # Robert Israel, Jan 18 2024
MATHEMATICA
PolygonalNumber[Select[Range[300], Divisible[#, Total[IntegerDigits[# (# + 1) / 2]]]&]] (* Paolo Xausa, Jan 18 2024 *)
CROSSREFS
Includes A037156.
Sequence in context: A014007 A074254 A122963 * A219884 A042309 A215757
KEYWORD
base,easy,nonn
AUTHOR
Amarnath Murthy, Feb 14 2002
EXTENSIONS
More terms from Sascha Kurz, Mar 18 2002
Offset corrected by Sean A. Irvine, Dec 17 2023
STATUS
approved