3,1

Number of anti-divisors concatenated to form a(n) is A066272(n). We may consider prime values of the concatenated anti-divisor sequence and we may iterate it, i.e. n, a(n), a(a(n)), a(a(a(n))) which leads to questions of trajectory, cycles, fixed points.

See A066272 for definition of anti-divisor.

Primes in this sequence are at n=3,4,5,10,14,16,40,46,100,145,149,... - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 24 2007

Jon Perry, The Anti-Divisor, cached copy.

J. V. Post, Factors of first 62 terms

3: 2, so a(3) = 2.

4: 3, so a(4) = 3.

5: 2, 3, so a(5) = 23.

6: 4, so a(6) = 4.

7: 2, 3, 5, so a(7) = 235.

17: 2, 3, 5, 7, 11, so a(17) = 235711

antiDivs := proc(n) local resul, odd2n, r ; resul := {} ; for r in ( numtheory[divisors](2*n-1) union numtheory[divisors](2*n+1) ) do if n mod r <> 0 and r> 1 and r < n then resul := resul union {r} ; fi ; od ; odd2n := numtheory[divisors](2*n) ; for r in odd2n do if ( r mod 2 = 1) and r > 2 then resul := resul union {2*n/r} ; fi ; od ; RETURN(resul) ; end: A130846 := proc(n) cat(op(antiDivs(n))) ; end: seq(A130846(n), n=3..80) ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 24 2007

Cf. A037278, A066272, A120712, A106708, A130799.

Sequence in context: A137077 A046965 A119679 this_sequence A114101 A114007 A071819

Adjacent sequences: A130843 A130844 A130845 this_sequence A130847 A130848 A130849

base,easy,nonn

Jonathan Vos Post (jvospost3(AT)gmail.com), Jul 20 2007, Jul 22 2007

More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 24 2007