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 A261066 #21 Feb 10 2025 20:49:02
%S A261066 6,150,180150,519264540150,8628341205030630049260150,
%T A261066 4764689404827483203666304150636608674826622242700150
%N A261066 a(n) = (7^(2^n) - 1) / 2^(n+2).
%C A261066 (m^(2^n)-1)/2^(n+2) is an integer for any odd value of m and n>0.
%C A261066 The next term, a(7), has 106 decimal digits.
%F A261066 a(n) == 150 (mod 10^4) for all n > 1. - _M. F. Hasler_, Aug 11 2015
%e A261066 a(3) = (7^8 - 1)/2^5 = 180150.
%t A261066 Table[(7^(2^n) - 1)/2^(n + 2), {n, 1, 7}] (* _Vincenzo Librandi_, Aug 09 2015 *)
%o A261066 (PARI) first(m)=vector(m,i, (7^(2^i)-1)/2^(i+2)); /* _Anders Hellström_, Aug 08 2015 */
%o A261066 (Magma) [(7^(2^n)-1)/2^(n+2): n in [1..10]]; // _Vincenzo Librandi_, Aug 09 2015
%o A261066 (PARI) A261066(n)=7^2^n>>(n+2) \\ _M. F. Hasler_, Aug 11 2015
%Y A261066 Cf. A059723, A068531, A097421. Twice A359500.
%K A261066 nonn
%O A261066 1,1
%A A261066 _Marco Ripà_, Aug 08 2015
%E A261066 a(5) corrected by _Vincenzo Librandi_, Aug 09 2015