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!)
 A093550 a(n) is the smallest number m such that each of the numbers m-1, m and m+1 is a product of n distinct primes. 12
 34, 1310, 203434, 16467034, 1990586014, 41704979954, 102099792179230, 22192526378762466 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS Each term of this sequence is of the form 4k+2. LINKS Jacques Tramu, Puzzle 371 EXAMPLE a(5)=16467034 because each of the three numbers 16467034-1, 16467034 & 16467034+1 are products of 5 distinct primes (16467033=3*11*17*149*197, 16467034=2*19*23*83*227, 16467035=5*13*37*41*167) and 16467034 is the smallest such number. MATHEMATICA a[n_] := a[n] = (For[m=1, !(Length[FactorInteger[4m+1]]==n && SquareFreeQ[4m+1] && Length[FactorInteger[4m+2]]==n && SquareFreeQ[4m+2] && Length[FactorInteger[4m+3]]==n && SquareFreeQ[4m+3]), m++ ]; 4m+2); Table[Print[a[n]]; a[n], {n, 2, 6}] (* updated by Jean-François Alcover, Jul 04 2013 *) PROG (PARI) a(n)={my(m=1); while(!(issquarefree(m-1)&&issquarefree(m)&&issquarefree(m+1)&&omega(m-1)==n&&omega(m)==n&&omega(m+1)==n), m++); return(m); } main(size)={my(n); return(vector(size, n, a(n+1))); } /* Anders Hellström, Jul 14 2015 */ CROSSREFS Cf. A093549, A052215, A093548, A248201, A248202, A248203, A248204, A259349, A259350, A259801. Sequence in context: A251924 A158731 A297693 * A296587 A212735 A123790 Adjacent sequences:  A093547 A093548 A093549 * A093551 A093552 A093553 KEYWORD more,nonn AUTHOR Farideh Firoozbakht, Apr 07 2004, corrected Aug 26 2006 EXTENSIONS a(7) added from Jacques Tramu's web site by Farideh Firoozbakht, Aug 26 2006 a(8) from Donovan Johnson, Oct 27 2008 a(9) from James G. Merickel, Jul 24 2015 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 April 18 10:56 EDT 2021. Contains 343087 sequences. (Running on oeis4.)