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A280693 Numbers n such that A003961(n) = A250469(n). 4
1, 2, 3, 4, 5, 6, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 29, 31, 35, 37, 41, 43, 47, 49, 50, 52, 53, 55, 59, 61, 65, 66, 67, 71, 73, 77, 79, 83, 85, 89, 91, 95, 97, 101, 103, 107, 109, 113, 115, 119, 121, 127, 131, 133, 137, 139, 143, 149, 151, 157, 161, 163, 167, 169, 173, 179, 181, 186, 187, 191, 193, 197, 199, 203 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Positions of zeros in A280692. Conjectured to be also the positions of ones in A280703.

For most terms k of this sequence A003961(k) is also included as a term. Exceptions are: 50, 52, 66, 186, 435, 1245, 1445, 2068, 2085, 11605, ... that seems to be a subsequence of all those terms that have more than two prime factors: 50, 52, 66, 186, 435, 1245, 1445, 2068, 2085, 8695, 11605, ...

Note how 8695 = 5*37*47 and A003961(8695) = 7*41*53 = 15211 = A003961(8695) = A250469(8695) (for no apparent reason?).

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..2001

MATHEMATICA

f[n_] := f[n] = Which[n == 1, 1, PrimeQ@ n, NextPrime@ n, True, Times @@ Replace[FactorInteger[n], {p_, e_} :> f[p]^e, 1]]; g[n_] := If[n == 1, 0, PrimePi@ FactorInteger[n][[1, 1]]]; With[{nn = 204}, Function[s, Function[t, Select[Range@ nn, f@ # == t[[#]] &]]@ MapIndexed[Lookup[s, g[First@ #2] + 1][[#1]] - Boole[First@ #2 == 1] &, #] &@ Map[Position[Lookup[s, g@ #], #][[1, 1]] &, Range@ nn]]@ PositionIndex@ Array[g, 10^4]] (* Michael De Vlieger, Mar 08 2017, Version 10 *)

PROG

(Scheme, with Antti Karttunen's IntSeq-library)

(define A280693 (ZERO-POS 1 1 A280692))

CROSSREFS

Fixed points of permutations A266645 & A266646.

Cf. A001222, A003961, A250469, A280692, A280703.

Cf. A000040, A001248, A006094, A251728 (subsequences).

Cf. also arrays A083221 and A246278.

Sequence in context: A033059 A031876 A292621 * A281613 A174738 A011867

Adjacent sequences:  A280690 A280691 A280692 * A280694 A280695 A280696

KEYWORD

nonn

AUTHOR

Antti Karttunen, Mar 08 2017

STATUS

approved

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Last modified September 21 07:08 EDT 2019. Contains 327253 sequences. (Running on oeis4.)