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A227006
Numbers n such that n-1 is not squarefree or a prime divisor of n-1 is in the sequence.
6
5, 6, 9, 10, 11, 12, 13, 14, 16, 17, 18, 19, 20, 21, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75
OFFSET
1,1
COMMENTS
The sequence is defined recursively. The complement of A227007.
FORMULA
a(n) = n + 16 for n > 1791. - Charles R Greathouse IV, Jun 27 2013
MATHEMATICA
Needs["NumberTheory`NumberTheoryFunctions`"]; Property[2] = False; Property[{}] = False; Property[n_] := Property[n] = If[ListQ[n], Property[n[[1, 1]]] || Property[Rest[n]], SquareFreeQ[n - 1] == False || Property[fa[n - 1]]]; Select[1 + Range[100], Property]
PROG
(PARI) is(n)=if(n<7, return(n>4)); if(n>1807 || !issquarefree(n-1), return(1)); fordiv(n-1, d, if(isprime(d) && is(d), return(1))); 0 \\ Charles R Greathouse IV, Nov 13 2013
CROSSREFS
Cf. A227007.
Sequence in context: A260635 A306016 A087176 * A139454 A049329 A195925
KEYWORD
nonn,easy
AUTHOR
EXTENSIONS
Definition corrected by Charles R Greathouse IV, Nov 13 2013
STATUS
approved