This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A362680 #38 Apr 17 2025 01:57:48
%S A362680 1,3,5,7,9,11,13,15,17,20,24,28,32,36,40,44,48,52,56,60,64,68,72,76,
%T A362680 80,84,88,92,96,100,104,108,112,116,120,124,128,132,136,140,144,148,
%U A362680 152,156,160,164,168,172,176,180,184,188,192,196,200,204,208,212,216,220,224,228,232
%N A362680 a(n) is the number of decimal digits in A173426(n).
%H A362680 Stefano Spezia, <a href="/A362680/b362680.txt">Table of n, a(n) for n = 1..5000</a>
%F A362680 a(n) = A058183(n) + A058183(n-1), for n >= 2.
%F A362680 a(n) = A055642(A173426(n)).
%F A362680 a(n) = 2*A058183(n) - A055642(n).
%e A362680 a(12)=28 since 1234567891011121110987654321 has 28 digits.
%t A362680 a[n_]:=IntegerLength[FromDigits[Flatten[IntegerDigits/@Join[Range[n], Reverse[Range[n-1]]]]]]; Array[a,63] (* _Stefano Spezia_, Apr 16 2025 *)
%o A362680 (PARI)
%o A362680 a(n)={my(t=logint(n,10)+1); 2*n*t-2*(10^t-1)/9+t}
%o A362680 (Python)
%o A362680 def a(n): return ((n*(t:=len(str(n)))-(10**t-1)//9)<<1) + t
%o A362680 print([a(n) for n in range(1, 64)]) # _Michael S. Branicky_, May 02 2023
%Y A362680 Cf. A173426, A058183, A055642.
%K A362680 nonn,base,easy
%O A362680 1,2
%A A362680 _David Cleaver_, Apr 29 2023