A209191 - OEIS

A209191

Numbers k such that digital root of k equals smallest prime factor of k.

2, 3, 5, 7, 20, 21, 38, 39, 56, 57, 74, 75, 92, 93, 95, 110, 111, 128, 129, 133, 146, 147, 164, 165, 182, 183, 185, 200, 201, 218, 219, 236, 237, 254, 255, 259, 272, 273, 275, 290, 291, 308, 309, 326, 327, 344, 345, 362, 363, 365, 380, 381, 398, 399, 416, 417

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

Numbers k such that A010888(k) = A020639(k). - Jason Yuen, Sep 17 2025

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

PrimeFan, Listing of Esoteric Integer Sequences

PrimeFan, Esoteric Integer Sequences [Cached copy]

MATHEMATICA

drspfQ[n_]:=NestWhile[Total[IntegerDigits[#]]&, n, #>9&] == FactorInteger[ n][[1, 1]]; Select[Range[2, 400], drspfQ] (* Harvey P. Dale, Nov 11 2017 *)

CROSSREFS

Cf. A010888, A020639.

Sequence in context: A048405 A110457 A320584 * A162948 A024768 A024769

Adjacent sequences: A209188 A209189 A209190 * A209192 A209193 A209194

KEYWORD

nonn,base

AUTHOR

N. J. A. Sloane, Mar 05 2012

EXTENSIONS

Prior Mathematica program replaced by Harvey P. Dale, Nov 11 2017

STATUS

approved