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.

1, 9, 10, 91, 28, 54, 191, 1000, 9001, 1089, 8712, 3466, 3177, 4536, 1818, 6363, 7273, 6454, 8092, 4816, 1368, 7263, 6364, 8272, 4456, 2088, 6714, 7462, 5185, 630, 406, 198, 693, 703, 604, 802, 1278, 7443, 6004, 8002, 4006, 1998, 6993, 7003, 16004, 24057, 50985, 7920, 2377, 5355, 180

Offset

1,2

Links

Table of n, a(n) for n=1..51.

Example

a(1), read backwards, is  1, which is present in a(1) + a(2) =  1+ 9 =  10;
a(2), read backwards, is  9, which is present in a(2) + a(3) =  9+10 =  19;
a(3), read backwards, is 01, which is present in a(3) + a(4) = 10+91 = 101;
a(4), read backwards, is 19, which is present in a(4) + a(5) = 91+28 = 119; etc.

Mathematica

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]

Prog

(Python)
from itertools import count, islice
def agen(): # generator of terms
    an, aset, mink = 1, set(), 2
    while True:
        yield an; aset.add(an); t = str(an)[::-1]; mink = max(int(t)-an, 2)
        an = next(k for k in count(mink) if k not in aset and t in str(an+k))
print(list(islice(agen(), 51))) # Michael S. Branicky, Oct 15 2023

Crossrefs

Cf. A004086.

Sequence in context: A136874 A136881 A333402 * A248306 A336690 A375790

Adjacent sequences: A360944 A360945 A360946 * A360948 A360949 A360950

Keyword

base,nonn

Author

Eric Angelini and Giorgos Kalogeropoulos, Oct 15 2023

Status

approved