A226030 Smallest m such that A226029(m) = n.

1, 3, 15, 46, 4, 448, 1415, 13, 14143, 44722, 14, 447215, 45, 4472137, 14142137, 140, 141421357, 447213596, 1414213563, 4472135956, 14142135625, 44721359551, 141421356238, 447213595501, 1414213562374, 4472135955001, 14142135623732, 44721359549997, 141421356237311, 447213595499959

Offset

1,2

Comments

a(39) = 44. - Michel Marcus, Jan 26 2022

Let k = ceiling(sqrt(2*10^m)). Then some terms are of the form k or k + 1. - David A. Corneth, Jan 27 2022

Links

Table of n, a(n) for n=1..30.

Formula

A226029(a(n)) = n and A226029(m) <> n for m < a(n).

Prog

(Haskell)
import Data.List (elemIndex)
import Data.Maybe (fromJust)
a226030 = (+ 1) . fromJust . (`elemIndex` a226029_list)
(PARI) nb(n) = {my(x=n*(n-1)/2+1, y=n*(n+1)/2, nx=#Str(x), ny=#Str(y), s=0); for (i=nx, ny, if (i==nx, if (i==ny, s+=(y+1-x)*i, s+=(10^i-x)*i), if (i==ny, s+=(y+1-10^(i-1))*i, s+=i*(10^(i+1)-10^i+1)); ); ); s; } \\ A182402
a(n) = my(k=1, last=nb(k), new=nb(k+1)); while (new-last !=n, k++; last=new; new=nb(k+1)); k; \\ Michel Marcus, Jan 26 2022

Crossrefs

Cf. A068092, A182402, A226029.

Sequence in context: A261505 A331505 A088108 * A232077 A163383 A296799

Adjacent sequences: A226027 A226028 A226029 * A226031 A226032 A226033

Keyword

nonn

Author

Reinhard Zumkeller, May 26 2013

Extensions

a(12)-a(18) from Michel Marcus, Jan 26 2022

More terms from David A. Corneth, Jan 26 2022

Status

approved