A266999 Smallest number m such that A266998(m) = n.

1, 10, 4, 12, 6, 3, 2, 11, 5, 18, 7, 13, 9, 19, 8, 17, 115, 3789

Offset

0,2

Comments

The next term is too large to include.

Links

Michel Marcus, Table of n, a(n) for n = 0..17

Formula

A266998(a(n)) = n and A266998(m) != n for m < a(n).

Mathematica

a266999={};
f[n_]:=Total[IntegerDigits[n]*(IntegerDigits[n]+1)/2];
g[n_]:=NestWhileList[f[#]&, n, #>1&];
h[n_]:=Length[g[n]]-1;
a266998=h/@Range[10^6];
Do[AppendTo[a266999, First[Position[a266998, m]]], {m, 0, Max[a266998]}];
a266999//Flatten

Prog

(PARI) strd(n) = {my(d = digits(n)); sum(k=1, #d, d[k]*(d[k]+1)/2); }
nbi(n) = {my(nb=0); while(n != 1, n = strd(n); nb++; ); nb; }
a(n) = {my(m = 1); while(nbi(m) != n, m++); m; } \\ Michel Marcus, Jan 12 2016

Crossrefs

Cf. A266998.

Sequence in context: A309707 A100844 A076587 * A166204 A364190 A329649

Adjacent sequences: A266996 A266997 A266998 * A267000 A267001 A267002

Keyword

base,more,nonn

Author

Ivan N. Ianakiev, Jan 10 2016

Status

approved