The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A011772 Smallest number m such that m(m+1)/2 is divisible by n. 20
 1, 3, 2, 7, 4, 3, 6, 15, 8, 4, 10, 8, 12, 7, 5, 31, 16, 8, 18, 15, 6, 11, 22, 15, 24, 12, 26, 7, 28, 15, 30, 63, 11, 16, 14, 8, 36, 19, 12, 15, 40, 20, 42, 32, 9, 23, 46, 32, 48, 24, 17, 39, 52, 27, 10, 48, 18, 28, 58, 15, 60, 31, 27, 127, 25, 11, 66, 16, 23, 20, 70, 63, 72, 36, 24 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(2^k) = 2^(k+1)-1; a(m)=m-1 and for odd prime powers m. - Reinhard Zumkeller, Feb 26 2003 REFERENCES C. Ashbacher, The Pseudo-Smarandache Function and the Classical Functions of Number Theory, Smarandache Notions Journal, Vol. 9, No. 1-2, 1998, 79-82. LINKS T. D. Noe, Table of n, a(n) for n = 1..1000 Jason Earls, The Smarandache sum of composites between factors function, in Smarandache Notions Journal (2004), Vol. 14.1, page 246. K. Kashihara, Comments and Topics on Smarandache Notions and Problems, Erhus University Press, 1996, 50 pages. See p. 35. K. Kashihara, Comments and Topics on Smarandache Notions and Problems, Erhus University Press, 1996, 50 pages. [Cached copy] See p. 35. Eric Weisstein's World of Mathematics, Pseudosmarandache Function FORMULA a(n) <= 2n-1 for all numbers n; a(n) <= n-1 for odd n. - Stefan Steinerberger, Apr 03 2006 a(n) >= (sqrt(8n+1)-1)/2 for all n. - Charles R Greathouse IV, Jun 25 2017 MATHEMATICA Table[m := 1; While[Not[IntegerQ[(m*(m + 1))/(2n)]], m++ ]; m, {n, 1, 90}] (* Stefan Steinerberger, Apr 03 2006 *) (Sqrt[1+8#]-1)/2&/@Flatten[With[{r=Accumulate[Range]}, Table[ Select[r, Divisible[#, n]&, 1], {n, 80}]]] (* Harvey P. Dale, Feb 05 2012 *) PROG (Haskell) import Data.List (findIndex) import Data.Maybe (fromJust) a011772 n = (+ 1) \$ fromJust \$    findIndex ((== 0) . (`mod` n)) \$ tail a000217_list -- Reinhard Zumkeller, Mar 23 2013 (PARI) a(n)=if(n==1, return(1)); my(f=factor(if(n%2, n, 2*n)), step=vecmax(vector(#f~, i, f[i, 1]^f[i, 2]))); forstep(m=step, 2*n, step, if(m*(m-1)/2%n==0, return(m-1)); if(m*(m+1)/2%n==0, return(m))) \\ Charles R Greathouse IV, Jun 25 2017 CROSSREFS A066561(n)=A000217(a(n)). Cf. A080982. Sequence in context: A318457 A198501 A230072 * A060451 A220291 A129187 Adjacent sequences:  A011769 A011770 A011771 * A011773 A011774 A011775 KEYWORD nonn,easy,nice,changed AUTHOR Kenichiro Kashihara (Univxiq(AT)aol.com) EXTENSIONS More terms from Stefan Steinerberger, Apr 03 2006 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 12 17:17 EDT 2020. Contains 336439 sequences. (Running on oeis4.)