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A352822
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Number of fixed points y(i) = i, where y is the weakly increasing sequence of prime indices of n.
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28
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0, 1, 0, 1, 0, 2, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 2, 0, 2, 0, 1, 0, 1, 0, 1, 1, 1, 0, 3, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 2, 0, 1, 2, 1, 0, 1, 0, 2, 0, 1, 0, 2, 0, 2, 0, 1, 0, 1, 0, 1, 1, 1, 0, 2, 0, 1, 0, 1, 0, 1, 0, 1, 1, 1, 0, 2, 0, 1, 1, 1, 0, 2, 0, 1, 0, 1, 0, 2, 0, 1, 0, 1, 0, 1, 0, 1, 1, 2, 0, 2, 0, 1, 0
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OFFSET
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1,6
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COMMENTS
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A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.
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LINKS
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FORMULA
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EXAMPLE
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The prime indices of 6500 are {1,1,3,3,3,6} with fixed points at positions {1,3,6}, so a(6500) = 3.
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MAPLE
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f:= proc(n) local F, J, t;
F:= sort(ifactors(n)[2], (s, t) -> s[1]<t[1]);
J:= map(t -> numtheory:-pi(t[1])$t[2], F);
nops(select(t -> J[t]=t, [$1..nops(J)]));
end proc:
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MATHEMATICA
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pq[y_]:=Length[Select[Range[Length[y]], #==y[[#]]&]];
Table[pq[Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]], {n, 100}]
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PROG
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(PARI) A352822(n) = { my(f=factor(n), i=0, c=0); for(k=1, #f~, while(f[k, 2], f[k, 2]--; i++; c += (i==primepi(f[k, 1])))); (c); }; \\ Antti Karttunen, Apr 11 2022
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CROSSREFS
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* = unproved
Positions of first appearances are A002110.
A122111 represents partition conjugation using Heinz numbers.
A238395 counts reversed partitions with a fixed point, ranked by A352872.
Cf. A065770, A093641, A098825, A114088, A118199, A257990, A325163, A325164, A325169, A342192, A352486-A352491, A352829.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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