A257115 Smallest k such that none of k + 1, k + 3,... k + 2n - 1 are squarefree and all of k + 2, k + 4,... k + 2n are squarefree.

1, 3, 15, 15, 49, 483, 5049, 6347, 144945

Offset

0,2

Comments

For any x, one of x+2, x+4, ..., x+18 is divisible by 9 and thus not squarefree, so a(n) does not exist for n >= 9. - Robert Israel, Apr 27 2015

Links

Table of n, a(n) for n=0..8.

Example

a(0) = 1 because 1 + 0 = 1 is squarefree.
a(1) = 3 because 3 + 1 = 4 is not squarefree and 3 + 2 = 5 is squarefree.

Prog

(PARI) a(n)=k=1; while(k, c=0; for(i=1, n, if(!issquarefree(k+2*i-1)&&issquarefree(k+2*i), c++); if(issquarefree(k+2*i-1)||!issquarefree(k+2*i), c=0; break)); if(c==n, return(k)); k++)
vector(9, n, n--; a(n)) \\ Derek Orr, Apr 27 2015

Crossrefs

Cf. A257108, A257116.

Sequence in context: A289103 A289403 A289459 * A159983 A133227 A237628

Adjacent sequences: A257112 A257113 A257114 * A257116 A257117 A257118

Keyword

nonn,fini,full

Author

Juri-Stepan Gerasimov, Apr 25 2015

Extensions

Corrected and extended by Derek Orr, Apr 27 2015

Status

approved