Neil: > 3. > # BIN1 was introduced by Don Zagier (see M. Kaneko, > # "A recurrence formula for the Bernoulli numbers", > # Proc. Japan Acad., 71 A (1995), 192-193). > # It is an involution on the class of sequences a = [a_0, a_1, a_2, ...], > # sending a to b where b_n = (-1)^n Sum_{i=0..n} binomial(n+1,i+1) a_i. > BIN1:=proc(a) local b,i,j,k: > if whattype(a) <> list then RETURN([]); fi: > b:=[]: > for i to nops(a) do j:=i-1; b:=[op(b), (-1)^j*add( binomial(j+1,k+1)*a[k+1] , > k=0..j)]: od: > RETURN(b); > end: The sequence that shifts left under BIN1 is 1 1 -3 3 -1 -1 1 1 -3 3 -1 -1 1 1 -3 3 -1 -1 1 1... a repeating sequence. (No I'm not submitting it.) However, the sequence that shifts left twice under BIN1 1 1 1 -3 7 -11 17 -27 45 -75 123 -199 321 -519 841... looks more interesting. The definition suggests a generalization to BINk with binomial(n+k,i+k) in the definition. I noticed that BIN2 at least is also involutional. > (The signs could be omitted, but Zagier needed them for his application, so > i have left them in.) The unsigned transform applied to 2^n gives (3^(n+1)-1)/2 A003462(n+1). A040027(n+1) shifts left under the unsigned transform. > 4. > # The "Stirling-Bernoulli transform" maps a sequence b_0, b_1, b_2, ... > # to a sequence c_0, c_1, c_2, ..., where if B has o.g.f. B(x), c has > # e.g.f. exp(x)*B(1-exp(x)). [Yes, the ogf becomes an egf.] > # More explicitly, > # c_n = Sum_{m=0..n} (-1)^m*m!*Stirling2(n+1,m+1)*b_m. This can be described as: Multiply each term by n! Perform alternating sign Stirling transform Perform Binomial transform The sequence that shifts left: 1 1 0 -2 6 250 -27090 -20110502 100802987166... grows fast. Christian