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 A081735 #21 Dec 15 2022 12:24:38
%S A081735 1,3,4,5,7,11,13,17,19,23,25,29,30,31,37,41,43,47,49,53,59,61,67,71,
%T A081735 73,79,83,89,97,101,103,107,109,113,121,127,131,137,139,149,151,157,
%U A081735 163,167,169,173,179,181,191,193,197,199,211,223,227,229,233,239,241,251,257
%N A081735 Numbers k such that the k-th Motzkin number == 1 (mod k).
%C A081735 All odd primes and all squares of primes are in the sequence. First composite (and not square of prime) are : 30, 464, 902, 21475, ... (A081736). [_Scott R. Shannon_ points out that this comment is wrong, since 9 is missing. Are there other errors? The comment needs to checked and corrected. - _N. J. A. Sloane_, Dec 15 2022]
%H A081735 Charles R Greathouse IV, <a href="/A081735/b081735.txt">Table of n, a(n) for n = 1..1000</a>
%t A081735 motzkin[0] = 1; motzkin[n_] := motzkin[n] = motzkin[n - 1] + Sum[motzkin[k] * motzkin[n - k - 2], {k, 0, n - 2}]; Select[Range[250], # == 1 || Mod[motzkin[#], #] == 1 &] (* _Amiram Eldar_, May 23 2022 *)
%o A081735 (PARI) a001006(n) = polcoeff((1-x-sqrt((1-x)^2-4*x^2+x^3*O(x^n)))/(2*x^2), n);
%o A081735 for(n=1, 1e3, if((a001006(n)-1) % n == 0, print1(n, ", "))); \\ _Altug Alkan_, Jan 07 2016
%Y A081735 Cf. A001006, A081736.
%K A081735 nonn
%O A081735 1,2
%A A081735 _Benoit Cloitre_, Apr 06 2003
%E A081735 First term 1 prepended by _Altug Alkan_, Jan 07 2016