Numbers k such that k and the k-th triangular number T(k) = k*(k+1)/2 have only even digits.

Terms

a(0) =0a(1) =28a(2) =40a(3) =64a(4) =400a(5) =2828a(6) =4000a(7) =4064a(8) =6428a(9) =22840a(10) =24028a(11) =40000a(12) =202428a(13) =240028a(14) =400000a(15) =2040040a(16) =2400028a(17) =4000000a(18) =6422840a(19) =6428064a(20) =6646624a(21) =20044064a(22) =20202080a(23) =20400040a(24) =20406080a(25) =24000028a(26) =40000000a(27) =66400064a(28) =200042428a(29) =204000040