A211201 Smallest m such that (sum of binary digits of m*(m+1)/2) = n.

0, 1, 2, 6, 5, 10, 19, 22, 37, 77, 108, 165, 90, 313, 461, 620, 1252, 1957, 2610, 3237, 5654, 7797, 9818, 15797, 22245, 34725, 56723, 92634, 122330, 178540, 226838, 507571, 454045, 490426, 1480005, 2284378, 1482842, 2965594, 5931098, 10218573, 11096982, 21793257, 31317157

Offset: 0

Author

Reinhard Zumkeller, Feb 04 2013

Keywords

• nonn
• base

Links

• Donovan Johnson, Table of n, a(n) for n = 0..71 (terms < 2*10^12)

Crossrefs

Cf. A089999, A050493, A000217, A000120.

Programs

Haskell

import Data.List (elemIndex)
import Data.Maybe (fromJust)
a211201 = fromJust . (`elemIndex` a050493_list)

PARI

a(n) = my(m=0); while (hammingweight(m*(m+1)/2) != n, m++); m; \\ Michel Marcus, Jan 27 2022

Formula

A050493(a(n)) = n and A050493(m) <> n for m < a(n).