OFFSET
0,3
MATHEMATICA
seq={0}; f[n_]:=Total[IntegerDigits[n]*(IntegerDigits[n]+1)/2]; lst=f/@Range[10^5];
Do[AppendTo[seq, First[Position[lst, m]]], {m, 1, 100}]; seq//Flatten
PROG
(PARI) strd(n) = {my(d = digits(n)); sum(k=1, #d, d[k]*(d[k]+1)/2); }
a(n) = {m = 0; while(strd(m) != n, m++); m; } \\ Michel Marcus, Jan 13 2016
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Ivan N. Ianakiev, Jan 13 2016
STATUS
approved