OFFSET
1,1
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..100
EXAMPLE
17*(17+1)/2= 153 = 9*2^4 + 9 -> '10011001' -> '1001''1001', therefore 17 is a term.
MATHEMATICA
tisbQ[n_]:=Module[{idn=IntegerDigits[(n(n+1))/2, 2], len}, len=Length[idn]; EvenQ[ len]&&Take[idn, len/2]==Take[idn, -len/2]]; Select[Range[ 180000], tisbQ] (* Harvey P. Dale, Aug 08 2016 *)
PROG
(PARI) is(n)=my(L=#binary(n*=(n+1)/2)\2); n>>L==bitand(n, 2^L-1) \\ Charles R Greathouse IV, Mar 29 2013
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Reinhard Zumkeller, Apr 12 2004
STATUS
approved