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 A060291 #13 Jan 19 2021 03:58:34
%S A060291 7,8,21,60,278,1520,9583,61835,419705,3023007,22597508
%N A060291 Number of twin Harshads, including overlaps, whose sum is prime and where the 2nd Harshad is <= 10^n.
%F A060291 Generate the twin Harshads whose sum is prime. Count how many there are where the 2nd Harshad in the pair is <= to a consecutive power of 10.
%e A060291 a(1)=7 because there are 7 pairs of Harshads whose sum is prime and the 2nd Harshad in the pair is <= 10; these are 1+2=3, 2+3=5, 3+4=7, 5+6=11, 6+7=13, 8+9=17, 9+10=19. (Another sequence does not permit overlapping Harshad numbers.)
%t A060291 harshadQ[n_] := Divisible[n, Plus @@ IntegerDigits[n]]; c = 0; p = 10; s = {}; n = 0; k = 2; q1 = True; While[n < 6, q2 = harshadQ[k]; If[q1 && q2 && PrimeQ[2*k-1], c++; If[k > p, n++; AppendTo[s, c-1]; p *= 10]]; q1 = q2; k++]; s (* _Amiram Eldar_, Jan 19 2021 *)
%Y A060291 Cf. A060288, A060289, A060290, A005349, A060159.
%K A060291 nonn,base,more
%O A060291 1,1
%A A060291 _Enoch Haga_, Mar 24 2001
%E A060291 a(8)-a(11) from _Amiram Eldar_, Jan 19 2021