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A360947 a(n), read backwards, is present as a substring in a(n) + a(n+1). This is the lexicographically earliest sequence of distinct terms > 0 with this property. 0

%I #18 Oct 19 2023 23:34:23

%S 1,9,10,91,28,54,191,1000,9001,1089,8712,3466,3177,4536,1818,6363,

%T 7273,6454,8092,4816,1368,7263,6364,8272,4456,2088,6714,7462,5185,630,

%U 406,198,693,703,604,802,1278,7443,6004,8002,4006,1998,6993,7003,16004,24057,50985,7920,2377,5355,180

%N a(n), read backwards, is present as a substring in a(n) + a(n+1). This is the lexicographically earliest sequence of distinct terms > 0 with this property.

%e a(1), read backwards, is 1, which is present in a(1) + a(2) = 1+ 9 = 10;

%e a(2), read backwards, is 9, which is present in a(2) + a(3) = 9+10 = 19;

%e a(3), read backwards, is 01, which is present in a(3) + a(4) = 10+91 = 101;

%e a(4), read backwards, is 19, which is present in a(4) + a(5) = 91+28 = 119; etc.

%t a[1]=1;a[n_]:=a[n]=(k=1;While[MemberQ[Array[a,n-1],k]|| !StringContainsQ[ToString[a[n-1]+k],StringReverse@ToString@a[n-1]],k++];k); Array[a,51]

%o (Python)

%o from itertools import count, islice

%o def agen(): # generator of terms

%o an, aset, mink = 1, set(), 2

%o while True:

%o yield an; aset.add(an); t = str(an)[::-1]; mink = max(int(t)-an, 2)

%o an = next(k for k in count(mink) if k not in aset and t in str(an+k))

%o print(list(islice(agen(), 51))) # _Michael S. Branicky_, Oct 15 2023

%Y Cf. A004086.

%K base,nonn

%O 1,2

%A _Eric Angelini_ and _Giorgos Kalogeropoulos_, Oct 15 2023

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Last modified May 21 07:02 EDT 2024. Contains 372729 sequences. (Running on oeis4.)