OFFSET
1,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..20000
Audrey Baumheckel and Tamás Forgács, Guided by the primes -- an exploration of very triangular numbers, arXiv:2105.10354 [math.HO], 2021.
MAPLE
q:= n-> issqr(8*add(i, i=Bits[Split](n))+1):
select(q, [j*(j+1)/2$j=0..200])[]; # Alois P. Heinz, May 24 2021
MATHEMATICA
Select[Table[n*(n + 1)/2, {n, 0, 200}], IntegerQ @ Sqrt[8 * Plus @@ IntegerDigits[#, 2] + 1] &] (* Amiram Eldar, May 24 2021 *)
Select[Accumulate[Range[0, 200]], OddQ[Sqrt[8 DigitCount[#, 2, 1]+1]]&] (* Harvey P. Dale, Feb 19 2023 *)
PROG
(PARI) isok(n) = ispolygonal(n, 3) && ispolygonal(hammingweight(n), 3);
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Michel Marcus, May 24 2021
STATUS
approved