OFFSET
1,3
FORMULA
a(1) = a(2) = 1; for n>2, a(n) = Product_{i=3..n} A024816(i).
MATHEMATICA
FoldList[#1 #2 &, Table[Boole[n <= 2] + n (n + 1)/2 - DivisorSigma[1, n], {n, 19}]] (* Michael De Vlieger, Jan 11 2017 *)
PROG
(Magma) [1, 1] cat [&*[k*(k+1)/2 - SumOfDivisors(k): k in [3..n]]: n in [3..100]]
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Jan 11 2017
STATUS
approved