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A178492 Primitive elements of A006532, i.e., which are not product of earlier terms (> 1) in that sequence. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

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, ...}.

LINKS

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

EXAMPLE

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.

PROG

(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", "))

CROSSREFS

Sequence in context: A159345 A006532 A274870 * A005288 A143166 A268792

Adjacent sequences:  A178489 A178490 A178491 * A178493 A178494 A178495

KEYWORD

nonn

AUTHOR

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

STATUS

approved

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Last modified February 24 03:21 EST 2018. Contains 299595 sequences. (Running on oeis4.)