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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
Sequence in context: A251924 A158731 A297693 * A296587 A212735 A123790
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

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Last modified March 28 05:39 EDT 2024. Contains 371235 sequences. (Running on oeis4.)