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A136111 Positive integers n such that for every k in [n,n+1,n+2,n+3,n+4] we have sigma(k) coprime to k. +0
1
1, 575, 202605639573839041, 478502736827135487987972323577847681 (list; graph; listen)
OFFSET

1,2

COMMENT

Note that it is impossible to have three consecutive positive even integers which have odd sigma() values.

In order to have an odd sigma() value, the integer must be a square or twice a square; it's not too hard to see that three consecutive positive even integers can't each be a square or twice a square.

So any solution must have n odd, and among n+1 and n+3, one of them must be a square and the other must be twice a square.

Any other terms exceed 10^128.

CROSSREFS

Adjacent sequences: A136108 A136109 A136110 this_sequence A136112 A136113 A136114

Sequence in context: A027456 A027527 A069421 this_sequence A131982 A053969 A109101

KEYWORD

nonn

AUTHOR

Jack Brennen (jb(AT)brennen.net), Mar 17 2008

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Last modified January 7 17:35 EST 2009. Contains 152824 sequences.


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