A227006 Numbers n such that n-1 is not squarefree or a prime divisor of n-1 is in the sequence.

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.

Links

Table of n, a(n) for n=1..65.

Index entries for linear recurrences with constant coefficients, signature (2,-1).

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

Adjacent sequences: A227003 A227004 A227005 * A227007 A227008 A227009

Keyword

nonn,easy

Author

José María Grau Ribas, Jun 27 2013

Extensions

Definition corrected by Charles R Greathouse IV, Nov 13 2013

Status

approved