id:A069249 - OEIS Search Results

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n^2-phi(n)*sigma(n).

+0
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0, 1, 1, 2, 1, 12, 1, 4, 3, 28, 1, 32, 1, 52, 33, 8, 1, 90, 1, 64, 57, 124, 1, 96, 5, 172, 9, 112, 1, 324, 1, 16, 129, 292, 73, 204, 1, 364, 177, 160, 1, 612, 1, 256, 153, 532, 1, 320, 7, 640, 297, 352, 1, 756, 145, 256, 369, 844, 1, 912, 1, 964, 225, 32, 193, 1476, 1, 592 (list; graph; listen)

	OFFSET	`1,4`
	COMMENT	`Always >0 for n>0. a(n)=1 if n is prime.` `If p is a prime and k is a natural number then a(p^k)=p^(k-1) because a(p^k)=(p^k)^2-sigma(p^k)phi(p^k) =p^(2k)-(p-1)p^(k-1)*(p^(k+1)-1)/(p-1)=p^(k-1). If n is a composite number then a(n)>1 and a(1)=0, so n is prime iff a(n)=1. - Farideh Firoozbakht (f.firoozbakht(AT)math.ui.ac.ir), Nov 15 2005`
	LINKS	`T. D. Noe, Table of n, a(n) for n=1..10000`
	CROSSREFS	`Sequence in context: A066818 A005730 A112284 this_sequence A128247 A105608 A051190` `Adjacent sequences: A069246 A069247 A069248 this_sequence A069250 A069251 A069252`
	KEYWORD	`easy,nonn`
	AUTHOR	`Benoit Cloitre (benoit7848c(AT)orange.fr), Apr 13 2002`

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Last modified December 2 15:58 EST 2008. Contains 150992 sequences.

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