A035527 - OEIS

%I #14 Apr 16 2017 04:54:34

%S 1,6,28,270,496,672,1638,6200,8128,18620,30240,32760,173600,1089270,

%T 2229500,2457000,4713984,6051500,8506400,17428320,23088800,29410290,

%U 33550336,45532800,52141320,81695250,115048440,142990848,255428096

%N Harmonic seed numbers.

%C A harmonic number is a harmonic seed if it does not have a proper unitary divisor (a divisor d such that gcd(d,n/d)=1) which is harmonic.

%H Donovan Johnson, <a href="/A035527/b035527.txt">Table of n, a(n) for n = 1..138</a> (terms < 10^14)

%H G. L. Cohen and R. M. Sorli, <a href="http://www.fq.math.ca/Scanned/36-5/cohen.pdf">Harmonic seeds</a>, Fibonacci Quart., 36 No. 5 (1998) 386-390 MR1657575 (99j:11002)

%o (PARI) harm(n)=if(n<1,0,0==(sigma(n,0)*n)%sigma(n,1))

%o {a(n)=local(t);if(n<0,0,n=a(n-1); until(if(t=1,if(harm(n), fordiv(n,d, t*=((d==n)||(d==1)||(gcd(d,n/d)!=1)||!harm(d)));t,0)),n++);n)}

%Y Cf. A001599 for harmonic numbers.

%K nonn

%O 1,2

%A _Jeff Burch_

%E Offset corrected by _Donovan Johnson_, Aug 21 2012