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A093550
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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.
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12
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OFFSET
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2,1
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COMMENTS
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Each term of this sequence is of the form 4k+2.
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LINKS
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Table of n, a(n) for n=2..9.
Jacques Tramu, Puzzle 371
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EXAMPLE
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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.
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MATHEMATICA
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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 *)
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PROG
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(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 */
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CROSSREFS
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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
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KEYWORD
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more,nonn
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AUTHOR
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Farideh Firoozbakht, Apr 07 2004, corrected Aug 26 2006
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EXTENSIONS
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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
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STATUS
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approved
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