A178492 Primitive elements of A006532, i.e., which are not product of earlier terms (> 1) in that sequence.

1, 3, 22, 70, 81, 94, 115, 119, 170, 214, 217, 265, 310, 322, 343, 364, 382, 385, 400, 472, 497, 517, 527, 679, 710, 742, 745, 782, 820, 862, 884, 889, 935, 970, 1004, 1066, 1080, 1174, 1177, 1207, 1219, 1270, 1393, 1426, 1465, 1501, 1566, 1612, 1624, 1645

Offset: 1

Author

Farideh Firoozbakht and M. F. Hasler, Jun 10 2010

Keywords

• nonn

Comments

If a,b are coprime elements of A006532, their product is again in A006532. But there are some a,b which are not coprime and still a,b,a*b are in A006532: First examples are 820*{2860, 3340, 8580, 10020, 11620, ...}.

Examples

			The terms a(2)=3 and a(3)=22 are coprime elements of A006532, therefore 3*22=66 is a non-primitive element of A006532, and not listed in this sequence.
		

Links

• Donovan Johnson, Table of n, a(n) for n = 1..10000

Programs

PARI

for(n=1,1e4, issquare(sigma(n))||next; fordiv( n,d, d>1||next; d*d>n & break; issquare(sigma(d)) & issquare(sigma(n/d)) & next(2) ); print1(n","))