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A081084 Nonsquarefree numbers m such that rad(m+1)=rad(m)+1, where rad(m)=A007947(m) is the squarefree kernel of m. 2
8, 48, 224, 960, 65024, 261120, 1046528, 4190208, 268402688, 1073676288, 4294836224, 17179607040, 70368727400448, 4503599493152768, 18014398241046528, 72057593501057024, 288230375077969920 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For k >= 3, 2^k*(2^(k-2)-1) is in the sequence if and only if 2^(k-1)-1 and 2^(k-2)-1 are squarefree. So if m is a term, m+1=2^(k-1)-1 is a squarefree number squared. - Lambert Herrgesell (zero815(AT)googlemail.com), Feb 18 2007

REFERENCES

J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 48, p. 18, Ellipses, Paris 2008.

LINKS

Table of n, a(n) for n=1..17.

EXAMPLE

48 = 2^4*3 is in the sequence because it is not squarefree, its squarefree kernel is 6 and the squarefree kernel of 49 = 7^2 is 7.

MAPLE

with(numtheory): rad:=proc(n) local fs, c: fs:=convert(factorset(n), list): c:=nops(fs): product(fs[j], j=1..c) end: b:=proc(n) if mobius(n)=0 and rad(n+1)=rad(n)+1 then n else fi end:seq(b(n), n=1..1000); # Emeric Deutsch

PROG

(PARI) rad(n)=my(f=factor(n)[, 1]); prod(i=1, #f, f[i])

is(n)=!issquarefree(n) && rad(n+1)==rad(n)+1 \\ Charles R Greathouse IV, Aug 08 2013

CROSSREFS

Cf. A081083, A062503.

Sequence in context: A087914 A271061 A211012 * A230931 A073390 A069021

Adjacent sequences:  A081081 A081082 A081083 * A081085 A081086 A081087

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Mar 04 2003

EXTENSIONS

a(5)-a(8) from Emeric Deutsch, Mar 29 2005

Edited and a(9) onwards supplied by Lambert Herrgesell (zero815(AT)googlemail.com), Feb 18 2007

STATUS

approved

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Last modified November 27 19:26 EST 2021. Contains 349394 sequences. (Running on oeis4.)