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 A309904 #11 Aug 26 2019 11:22:10
%S A309904 0,1,8,204,890,890,51311,286609,3580781,20875184,182289612,747240110,
%T A309904 8656547082,8656547082,105545557489,783768630338,15026453160167,
%U A309904 114725244868970,1045247300817798,9187315290370043,20586210475743186,20586210475743186
%N A309904 Approximation of the 7-adic integer exp(7) up to 7^n.
%C A309904 In p-adic field, the exponential function exp(x) is defined as Sum_{k>=0} x^k/k!. When extended to a function over the metric completion of the p-adic field, exp(x) has radius of convergence p^(-1/(p-1)) (i.e., exp(x) converges for x such that |x|_p < p^(-1/(p-1)), where |x|_p is the p-adic metric). As a result, for odd primes p, exp(p) is well-defined in p-adic field, and exp(4) is well defined in 2-adic field.
%C A309904 a(n) is the multiplicative inverse of A309905(n) modulo 7^n.
%H A309904 Wikipedia, <a href="https://en.wikipedia.org/wiki/P-adic_number">p-adic number</a>
%o A309904 (PARI) a(n) = lift(exp(7 + O(7^n)))
%Y A309904 Cf. A309905.
%Y A309904 The 7-adic expansion of exp(7) is given by A309987.
%Y A309904 Approximations of exp(p) in p-adic field: A309900 (p=3), A309902 (p=5), this sequence (p=7).
%K A309904 nonn
%O A309904 0,3
%A A309904 _Jianing Song_, Aug 21 2019