A035527 Harmonic seed numbers.

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

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