# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a280693 Showing 1-1 of 1 %I A280693 #20 Mar 09 2017 09:57:50 %S A280693 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, %T A280693 52,53,55,59,61,65,66,67,71,73,77,79,83,85,89,91,95,97,101,103,107, %U A280693 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 %N A280693 Numbers n such that A003961(n) = A250469(n). %C A280693 Positions of zeros in A280692. Conjectured to be also the positions of ones in A280703. %C A280693 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, ... %C A280693 Note how 8695 = 5*37*47 and A003961(8695) = 7*41*53 = 15211 = A003961(8695) = A250469(8695) (for no apparent reason?). %H A280693 Antti Karttunen, Table of n, a(n) for n = 1..2001 %t A280693 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 *) %o A280693 (Scheme, with _Antti Karttunen_'s IntSeq-library) %o A280693 (define A280693 (ZERO-POS 1 1 A280692)) %Y A280693 Fixed points of permutations A266645 & A266646. %Y A280693 Cf. A001222, A003961, A250469, A280692, A280703. %Y A280693 Cf. A000040, A001248, A006094, A251728 (subsequences). %Y A280693 Cf. also arrays A083221 and A246278. %K A280693 nonn %O A280693 1,2 %A A280693 _Antti Karttunen_, Mar 08 2017 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE