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A195008 Numbers n such that there are no primes between n*sqrt(n-1) and (n+1)*sqrt(n). 1
1, 24, 36, 47, 93, 105, 109, 117, 122, 207, 627, 996 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that there are only nonprimes between n*sqrt(n-1) and (n+1)*sqrt(n).

No more terms up to 100000. - Franklin T. Adams-Watters, Sep 08 2011

LINKS

Table of n, a(n) for n=1..12.

EXAMPLE

a(1)=1 because 1*sqrt(1-1)=0<(nonprime 1)<(1+1)*sqrt(1)=2,

a(2)=24 because 24*sqrt(24-1)<(nonprimes 116,117,118,119,120,121)<(24+1)*sqrt(24).

MATHEMATICA

Join[{1}, Select[Range[1000], PrimePi[# Sqrt[#-1]]==PrimePi[(#+1)Sqrt[#]]&]] (* Harvey P. Dale, Jun 01 2018 *)

PROG

(PARI) isa(n)=if(n<=1, n==1, primepi(floor(n*sqrt(n-1)))==primepi(floor((n+1)*sqrt(n)))

CROSSREFS

Cf. A195007

Sequence in context: A307682 A290016 A330880 * A054775 A273088 A334674

Adjacent sequences:  A195005 A195006 A195007 * A195009 A195010 A195011

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Sep 07 2011

EXTENSIONS

a(11) and a(12) from Franklin T. Adams-Watters, Sep 08 2011

STATUS

approved

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Last modified September 30 22:26 EDT 2020. Contains 337440 sequences. (Running on oeis4.)