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A035527 Harmonic seed numbers. 3
1, 6, 28, 270, 496, 672, 1638, 6200, 8128, 18620, 30240, 32760, 173600, 1089270, 2229500, 2457000, 4713984, 6051500, 8506400, 17428320, 23088800, 29410290, 33550336, 45532800, 52141320, 81695250, 115048440, 142990848, 255428096 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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.

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..138 (terms < 10^14)

G. L. Cohen and R. M. Sorli, Harmonic seeds, Fibonacci Quart., 36 No. 5 (1998) 386-390 MR1657575 (99j:11002)

PROG

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

{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)}

CROSSREFS

Cf. A001599 for harmonic numbers.

Sequence in context: A281003 A049603 A333927 * A220437 A332465 A335290

Adjacent sequences:  A035524 A035525 A035526 * A035528 A035529 A035530

KEYWORD

nonn

AUTHOR

Jeff Burch

EXTENSIONS

Offset corrected by Donovan Johnson, Aug 21 2012

STATUS

approved

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Last modified July 13 13:48 EDT 2020. Contains 335688 sequences. (Running on oeis4.)