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A330129
a(n) is the last term of the analogous sequence to A121805, but with initial term n, or -1 if that sequence is infinite.
17
99999945, 9999999999999918, 36, 9999945, 999945, 9999999999999999936, 936, 9999999999972, 999999936, 999936, 999936, 99999945, 999954, 999918, 72, 99999918, 999999999927, 18, 999981, 999999999999999963, 99981, 999999999999999963, 999936, 9999999999999918, 9963
OFFSET
1,1
COMMENTS
The numbers of terms of the corresponding sequences are in A330128.
LINKS
Eric Angelini, Michael S. Branicky, Giovanni Resta, N. J. A. Sloane, and David W. Wilson, The Comma Sequence: A Simple Sequence With Bizarre Properties, arXiv:2401.14346, Youtube
MATHEMATICA
nxt[x_] := Block[{p=1, n=x}, While[n >= 10, n = Floor[n/10]; p *= 10]; p (n + 1)]; a[n_] := Block[{nT=1, nX=n, w1, w2, w3, x, it, stp, oX}, stp = 100; w1 = w2 = w3 = 0; While[True, oX = nX; nT++; x = 10*Mod[oX, 10]; nX = SelectFirst[Range[9], IntegerDigits[oX + x + #][[1]] == # &, 0]; If[nX == 0, Break[], nX = nX + oX + x]; If[nT == stp, stp += 100; w1=w2; w2=w3; w3=nX; If[w3 + w1 == 2 w2 && Mod[w3 - w2, 100] == 0, it = Floor[(nxt[nX] - nX - 1)/(w3 - w2)]; nT += it*100; nX += (w3 - w2)*it; w3=nX; stp += it*100]]]; oX]; Array[a, 30]
PROG
(Python)
def nxt(x):
p, n = 1, x
while n >= 10:
n //= 10
p *= 10
return p * (n + 1)
def a(n):
nT, nX, w1, w2, w3, stp = 1, n, 0, 0, 0, 100
while True:
oX = nX
nT += 1
x = 10*(oX%10)
nX = next((y for y in range(1, 10) if str(oX+x+y)[0] == str(y)), 0)
if nX == 0: break
else: nX += oX + x
if nT == stp:
stp += 100
w1, w2, w3 = w2, w3, nX
if w3 + w1 == 2*w2 and (w3 - w2)%100 == 0:
it = (nxt(nX) - nX - 1)//(w3 - w2)
nT += it*100
nX += (w3 - w2)*it
w3 = nX
stp += it*100
return oX
print([a(n) for n in range(1, 30)]) # Michael S. Branicky, Nov 18 2023 after Giovanni Resta
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Giovanni Resta, Dec 02 2019
EXTENSIONS
Escape clause added to definition by N. J. A. Sloane, Nov 14 2023
STATUS
approved