A290224 - OEIS

%I #4 Jul 24 2017 12:31:28

%S 1,19,81,162,181,199,243,262,324,343,405,424,486,505,567,648,685,729,

%T 766,810,847,891,910,928,972,1053,1072,1134,1153,1215,1234,1296,1315,

%U 1377,1458,1495,1539,1576,1620,1657,1701,1720,1738,1782,1801,1819,1863,1944,1981,1999,2025,2044,2106,2125,2187,2206,2268

%N Numbers n such that A290223(n) = 0.

%C This sequence is believed to be infinite.

%e 181 is in this sequence because 181 - (1+8+1)^2 = 81. Then 81 - (8+1)^2 = 0.

%o (PARI)

%o a(n)=k=n; c=1; v=List(); listput(v, k); while(c, if(k>=0, k-=sumdigits(k)^2; c+=1; if(k==2||k==3||k==0||k==6||k==9, return(k)); if(vecsearch(Vec(v), k), return(sumdigits(abs(k)))); listput(v, k)); if(k<0, k+=sumdigits(-k)^2; c+=1; if(k==2||k==3||k==0||k==6||k==9, return(k)); if(vecsearch(Vec(v), k), return(sumdigits(abs(k)))); listput(v, k)); c+=1)

%o for(n=1,10^4,if(a(n)==0,print1(n,", ")))

%Y Cf. A007953, A003132, A290223.

%K nonn,base

%O 1,2

%A _Derek Orr_, Jul 24 2017