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 A187553 #13 Mar 30 2012 18:35:54 %S A187553 0,11,0,2,101111,211,2111,101111111,3,13,113,112121,23,21221,1123, %T A187553 11213,41,1223,313,10133,241,233,112223,21313,5,431,151,1151,13313, %U A187553 251,2333,11251,2243,53,1433,1153,61,523,1523,11161,443,541,353,33413,2621,163,1163,13523,7,17 %N A187553 Smallest prime p such that the sum of the squares of the digits of p equals n (or 0 if no such prime exists). %C A187553 a(3) = 0 because the numbers of the form 10..010..01 are divisible by 3. Conjecture : except for the numbers 1 and 3, for every possible square digit sum there exists a prime. %e A187553 a(13) = 23 because 2^2 + 3^2 = 13, and 23 is the least such prime. %p A187553 with(numtheory):for k from 2 to 100 do: id:=0:for p from 1 to 100000 while(id=0) %p A187553 do:n:=ithprime(p):l:=length(n):n0:=n:s:=0:for m from 1 to l do:q:=n0:u:=irem(q,10):v:=iquo(q,10):n0:=v :s:=s+u^2:od: if s=k then id:=1:printf(`%d, `,n):else fi:od:od: %Y A187553 Cf. A003132, A020449, A055016, A067180. %K A187553 nonn,base %O A187553 1,2 %A A187553 _Michel Lagneau_, Mar 26 2011