OFFSET
1,2
LINKS
S. S. Gupta, Can You Find (CYF) no. 55, Nov 11 2021.
FORMULA
a(n) = floor(sqrt(2*A117960(n))).
MAPLE
a:= proc(n) option remember; local k; for k from
1+`if`(n=1, 0, b(n-1)) while 0=mul(irem(i, 2),
i=convert(k*(k+1)/2, base, 10)) do od; k
end:
seq(a(n), n=1..57); # Alois P. Heinz, Nov 22 2021
MATHEMATICA
Select[Range[4000], AllTrue[IntegerDigits[#*(# + 1)/2], OddQ] &] (* Amiram Eldar, Nov 20 2021 *)
Position[Accumulate[Range[4000]], _?(AllTrue[IntegerDigits[#], OddQ]&)]//Flatten (* Harvey P. Dale, Sep 06 2023 *)
PROG
CROSSREFS
KEYWORD
nonn,base
AUTHOR
M. F. Hasler, Nov 20 2021
STATUS
approved