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 A290788 #37 Apr 14 2021 22:41:53 %S A290788 6,56,656,8656,38656,238656,7238656,47238656,447238656,7447238656, %T A290788 27447238656,227447238656,3227447238656 %N A290788 Values of n such that 6^n ends in n, or expomorphic numbers in "base" 6. %C A290788 Definition: For positive integers b (as base) and n, the positive integer (allowing initial 0's) a(n) is expomorphic relative to base b (here 6) if a(n) has exactly n decimal digits and if b^a(n) == a(n) (mod 10^n) or, equivalently, b^a(n) ends in a(n). [See Crux Mathematicorum link.] %H A290788 Charles W. Trigg, <a href="https://cms.math.ca/publications/crux/issue/?volume=7&issue=6">Problem 559</a>, Crux Mathematicorum, page 192, Vol. 7, Jun. 81. %e A290788 6^6 = 46656 ends in 6, so 6 is a term. %e A290788 6^56 = ...656 ends in 56, so 56 is another term. %t A290788 Select[Range[10^6], PowerMod[6, #, 10^(1 + Floor@ Log10[#])] == # &] (* _Michael De Vlieger_, Apr 13 2021 *) %o A290788 (PARI) is(n)=my(m=10^#digits(n)); Mod(6,m)^n==n \\ _Charles R Greathouse IV_, Aug 10 2017 %Y A290788 Cf. A064541 (base 2), A183613 (base 3), A288845 (base 4), A289138, A306570 (base 5), A306686 (base 9). %Y A290788 Cf. A003226 (automorphic numbers), A033819 (trimorphic numbers). %K A290788 nonn,base,more %O A290788 1,1 %A A290788 _Bernard Schott_, Aug 10 2017 %E A290788 a(6)-a(9) from _Charles R Greathouse IV_, Aug 10 2017 %E A290788 a(10)-a(13) from _Chai Wah Wu_, Apr 13 2021