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Search: id:A072006
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| A072006 |
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Number of terms in InversePhi set of p[n]*(p[n]-1)=Phi[p[n]^2], where p[n] is the n-th prime and Phi=A000010. |
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+0
1
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| 3, 4, 5, 4, 2, 7, 5, 2, 2, 2, 2, 6, 10, 2, 2, 2, 2, 7, 4, 2, 16, 4, 2, 8, 19, 5, 2, 2, 2, 13, 2, 2, 2, 4, 5, 4, 2, 4, 2, 5, 2, 14, 2, 21, 2, 2, 2, 2, 2, 5, 5, 2, 28, 2, 2, 2, 2, 2, 8, 8, 2, 2, 2, 2, 4, 5, 2, 14, 2, 7, 5, 2, 2, 5, 4, 2, 2, 11, 7, 17, 2, 11, 2, 26, 2, 2, 12, 4, 5, 2, 2, 2, 2, 2, 2, 2, 5, 5
(list; graph; listen)
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OFFSET
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1,1
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FORMULA
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a(n)=Card[{InvPhi[p[n](p[n]-1)]}=Card[InvPhi(A036689(n)]
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EXAMPLE
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p^2 and 2p^2 are always in inverse set, so a(n)>=2; n=6:p(6)=13, a(6)=7 because InvPhi[13.12]=InvPhi[156]= {157, 169, 237, 314, 316, 338, 474}; n=5:p(5)=11, a(5)=2, InvPhi[110]={121, 242}
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MAPLE
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>[seq(nops(invphi(ithprime(j)*(-1+ithprime(j)))), j=1..128)];
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CROSSREFS
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Cf. A036689, A000010.
Sequence in context: A126352 A094758 A100394 this_sequence A014238 A014250 A115051
Adjacent sequences: A072003 A072004 A072005 this_sequence A072007 A072008 A072009
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KEYWORD
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nonn
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AUTHOR
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Labos E. (labos(AT)ana.sote.hu), Jun 04 2002
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