A071364 -id:A071364 - cp's OEIS frontend

A336835 Number of iterations of x -> A003961(x) needed before the result is deficient (sigma(x) < 2x), when starting from x=n.

0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 2

Offset: 1

Antti Karttunen, Aug 07 2020

nonn

It holds that a(n) <= A336836(n) for all n, because sigma(n) <= A003961(n) for all n (see A286385 for a proof).
The first 3 occurs at n = 19399380, the first 4 at n = 195534950863140268380. See A336389.
If x and y are relatively prime (i.e., gcd(x,y) = 1), then a(x*y) >= max(a(x),a(y)). Compare to a similar comment in A336915.

			For n = 120, sigma(120) = 360 >= 2*120, thus 120 is not deficient, and we get the next number by applying the prime shift, A003961(120) = 945, and sigma(945) = 1920 >= 945*2, so neither 945 is deficient, so we prime shift once again, and A003961(945) = 9625, which is deficient, as sigma(9625) = 14976 < 2*9625. Thus after two iteration steps we encounter a deficient number, and therefore a(120) = 2.

Cf. A003961, A005100, A005940, A023196, A046523, A047802, A071364, A108951, A286385, A294934, A336834, A337474, A337475.
Cf. A336389 (position of the first occurrence of a term >= n).
Differs from A294936 for the first time at n=120.
Cf. also A246271, A252459, A336836 and A336915 for similar iterations.

Array[-1 + Length@ NestWhileList[If[# == 1, 1, Times @@ Map[#1^#2 & @@ # &, FactorInteger[#] /. {p_, e_} /; e > 0 :> {Prime[PrimePi@ p + 1], e}]] &, #, DivisorSigma[1, #] >= 2 # &] &, 120] (* Michael De Vlieger, Aug 27 2020 *)

A003961(n) = my(f = factor(n)); for (i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); factorback(f); \\ From A003961
A336835(n) = { my(i=0); while(sigma(n) >= (n+n), i++; n = A003961(n)); (i); };

If A294934(n) = 1, a(n) = 0, otherwise a(n) = 1 + a(A003961(n)).
From Antti Karttunen, Aug 21-Sep 01 2020: (Start)
For all n >= 1,
a(A046523(n)) >= a(n).
a(A071364(n)) >= a(n).
a(A108951(n)) = A337474(n).
a(A025487(n)) = A337475(n).
(End)

A077462 Prime factor configuration patterns.

Original entry on oeis.org

0, 1, 2, 2, 3, 2, 4, 2, 5, 3, 4, 2, 6, 2, 4, 4, 7, 2, 8, 2, 6, 4, 4, 2, 9, 3, 4, 5, 6, 2, 10, 2, 11, 4, 4, 4, 12, 2, 4, 4, 9, 2, 10, 2, 6, 6, 4, 2, 13, 3, 8, 4, 6, 2, 14, 4, 9, 4, 4, 2, 15, 2, 4, 6, 16, 4, 10, 2, 6, 4, 10, 2, 17, 2, 4, 8, 6, 4, 10, 2, 13, 7, 4

Offset: 0

Michael Somos, Nov 07 2002

Call two numbers equivalent if they have the same prime factorization exponents (in the same order). This sequence enumerates the equivalence classes.
A055932(a(n)) = A071364(n). - David Wasserman, Dec 21 2004
From Antti Karttunen, Jun 13 2018: (Start)
After a(0) = 0, this is the restricted growth sequence transform of A071364. The latter sequence is an "ordered variant" of A046523, and because A101296 is the rgs-transform of A046523, it follows that for all i, j: a(i) = a(j) => A101296(i) = A101296(j).
(End)

			12 = 2^2*3^1 has exponents {2,1}, and is the first number with that pattern, so its value is one more than the largest previous value; a(12) = 6. Contrast that with 18 = 2^1*3^2 having exponents {1,2}, which is different from {2,1}, so a(18) is not equal to a(12). - _Franklin T. Adams-Watters_, Aug 01 2012

Antti Karttunen, Table of n, a(n) for n = 0..100000 (terms 0..10000 from T. D. Noe)
S. Whealton, Prime Factor Configuration Pattern Numbers.

Cf. A037916, A071364, A101296, A290110, A300250.

One more than A079616.

fList = {{0}}; Join[{0, 1}, Table[e = Transpose[FactorInteger[n]][[2]]; pos = Position[fList, e]; If[pos == {}, AppendTo[fList, e]; Length[fList], pos[[1, 1]]], {n, 2, 100}]] (* T. D. Noe, Aug 01 2012 *)

a(n)=local(vn); if(n<1,return(0)); vn=factor(n)[,2]; for(i=1,n,if(vn==factor(i)[,2],return(#Set(vector(i,j,factor(j)[,2])))))

up_to = 100000;
rgs_transform(invec) = { my(om = Map(), outvec = vector(length(invec)), u=1); for(i=1, length(invec), if(mapisdefined(om,invec[i]), my(pp = mapget(om, invec[i])); outvec[i] = outvec[pp] , mapput(om,invec[i],i); outvec[i] = u; u++ )); outvec; };
A071364(n) = { my(f = factor(n)); for (i=1, #f~, f[i, 1] = prime(i)); factorback(f); }; \\ From A071364
v077462 = rgs_transform(vector(up_to,n,A071364(n)));
A077462(n) = if(!n,n,v077462[n]); \\ Antti Karttunen, Jun 13 2018

A336389 The least positive integer k for which A336835(k) >= n, where A336835(k) is the number of iterations of x -> A003961(x) needed before the result is deficient (sigma(x) < 2x), when starting from x=k.

Original entry on oeis.org

1, 6, 120, 19399380, 195534950863140268380, 538938984694949877040715541221415046162838700, 216487559804430601784907786655491617909711008142914104790481010259258659171900

Offset: 0

Antti Karttunen, Aug 07 2020

For n > 0, the least k such that for at least n-1 iterations of map x -> A003961(x), starting from x=k, x stays nondeficient. In other words, from each a(n) starts a chain of at least n nondeficient numbers (A023196) obtained by successive prime shifts, e.g, for a(3) we have: 19399380 -> 334639305 -> 5391411025, where -> stands for applying A003961, the prime shift towards larger primes.
After 1 all other terms here are even, because if an odd number k is nondeficient, then A064989(k) is nondeficient also, where A064989 is the prime shift towards smaller primes. Moreover, because A047802 is defined for every n >= 0, also this sequence is.
From Peter Munn, Aug 13 2020 (Start)
Upper bounds for a(4) and a(5) are:
a(4) <= 195534950863140268380 = A064989(A064989(A064989(20169691981106018776756331))) = A337202(3).
a(5) <= 538938984694949877040715541221415046162838700 = A064989^4((A047802(4)*17*19)/137).
(End)
From David A. Corneth, Aug 21 2020: (Start)
Subsequence of A025487.
Let prime(n)# be the n-th primorial number, A002110(n) = A034386(prime(n)). Then:
a(6) <= 191# * 7#;
a(7) <= 311# * 5#;
a(8) <= 457# * 5#.
(End)
That each term occurs in A025487 follows because (1), the abundancy index of prime(i)^e is larger than that of prime(i+1)^e, that is, sigma(prime(i)^e)/prime(i)^e > sigma(prime(i+1)^e)/prime(i+1)^e, and (2) because the abundancy index of p^(e+d) * q^e is larger than that of p^e * q^(e+d), where p and q are distinct primes, p < q, and e, d > 0. Thus, for any n, we can first find a "prime-factorization compressed version" of it, A071364(n), and then sort the exponents to the non-ascending order with A046523 (and actually, A046523(A071364(n)) = A046523(n), so we need to apply just A046523), to get a term x of A025487, that certainly have the abundancy index >= n [and this inequivalence stays same for their successive prime shifts as well, the abundancy index of A003961(x) being at least that of A003961(n), etc.], and as A046523(n) <= n for all n, it is guaranteed that the least k for which A336835(k) >= n are found from A025487, which is the range of A046523.

Cf. A003961, A005100, A023196, A025487, A047802, A108951, A246277, A329900, A336834, A336835, A337202, A337205, A337477, A337478.

From term a(2) = 120 onward a subsequence of A337386.

A003961(n) = my(f = factor(n)); for (i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); factorback(f); \\ From A003961
A336835(n) = { my(i=0); while(sigma(n) >= (n+n), i++; n = A003961(n)); (i); };
A336389(n) = for(i=1,oo,if(A336835(i)>=n,return(i)));

For n >= 0, A336835(a(n)) >= n.
For all n >= 1, a(n) <= A337202(n-1) [= 2*A246277(A047802(n-1))].
a(n) = A025487(A337477(n)).
a(n) = A108951(A337478(n)).

a(4) - a(6) from combined work of David A. Corneth and Peter Munn Aug 13-26 2020

A329600 Smallest number with the same set of distinct prime exponents as A108951(n).

Original entry on oeis.org

1, 2, 2, 4, 2, 12, 2, 8, 4, 12, 2, 24, 2, 12, 12, 16, 2, 72, 2, 24, 12, 12, 2, 48, 4, 12, 8, 24, 2, 360, 2, 32, 12, 12, 12, 144, 2, 12, 12, 48, 2, 360, 2, 24, 24, 12, 2, 96, 4, 72, 12, 24, 2, 432, 12, 48, 12, 12, 2, 720, 2, 12, 24, 64, 12, 360, 2, 24, 12, 360, 2, 288, 2, 12, 72, 24, 12, 360, 2, 96, 16, 12, 2, 720, 12, 12, 12, 48, 2, 2160, 12, 24, 12, 12, 12

Offset: 1

Antti Karttunen, Nov 17 2019

nonn

Antti Karttunen, Table of n, a(n) for n = 1..20000
Index entries for sequences computed from indices in prime factorization

Cf. A007947, A034386, A071364, A108951, A122111, A181819, A181821, A328400, A329607.

Cf. A077462 (rgs-transform, from its term a(1)=1 onward).

Array[Times @@ MapIndexed[Prime[#2[[1]]]^#1 &, Reverse[Flatten[Cases[FactorInteger[#], {p_, k_} :> Table[PrimePi[p], {k}]]]]] &[Times @@ FactorInteger[#][[All, 1]]] &@ If[# == 1, 1, Times @@ Prime@ FactorInteger[#][[All, -1]]] &[Times @@ Map[#1^#2 & @@ # &, FactorInteger[#] /. {p_, e_} /; e > 0 :> {Times @@ Prime@ Range@ PrimePi@ p, e}]] &, 105] (* Michael De Vlieger, Nov 18 2019, after Gus Wiseman at A181821 *)

A007947(n) = factorback(factorint(n)[, 1]);
A181819(n) = factorback(apply(e->prime(e),(factor(n)[,2])));
A181821(n) = { my(f=factor(n),p=0,m=1); forstep(i=#f~,1,-1,while(f[i,2], f[i,2]--; m *= (p=nextprime(p+1))^primepi(f[i,1]))); (m); };
A328400(n) = A181821(A007947(A181819(n)));
A034386(n) = prod(i=1, primepi(n), prime(i));
A108951(n) = { my(f=factor(n)); prod(i=1, #f~, A034386(f[i, 1])^f[i, 2]) };  \\ From A108951
A329600(n) = A328400(A108951(n));

a(n) = A328400(A108951(n)) = A181821(A007947(A122111(n)))

a(n) = A181821(A329607(n)) = A181821(A122111(A071364(n))).

A085079 Largest number with the prime signature of n using prime divisors of n.

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 18, 13, 14, 15, 16, 17, 18, 19, 50, 21, 22, 23, 54, 25, 26, 27, 98, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 250, 41, 42, 43, 242, 75, 46, 47, 162, 49, 50, 51, 338, 53, 54, 55, 686, 57, 58, 59, 150, 61, 62, 147, 64, 65, 66, 67, 578, 69, 70

Offset: 1

Amarnath Murthy, Jul 01 2003

nonn

Though a large number of initial terms match, this sequence is different from A069799. Example: a(1500) = a(2^2*3*5^3) = 5^3*3^2*2 = 2250, whereas A069799(1500) = 5^2*3*2^3 = 600.

The first term that is different from A069799 is a(18). - Ivan Neretin, Jul 29 2015

			20 = 2^2*5, hence a(20) = 5^2*2 = 50.

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Cf. A069799.

Cf. A027748, A124010, A089247, A071364, A046523.

import Data.List (sort)
a085079 n = product $ zipWith (^) (a027748_row n) (sort $ a124010_row n)
-- Reinhard Zumkeller, Apr 27 2013

Table[Times @@ ((ar = Transpose[FactorInteger[n]])[[1]]^Sort[ar[[2]]]), {n, 70}] (* Ivan Neretin, Jul 29 2015*)
fise[n_]:=Module[{fi=FactorInteger[n]},Times@@(fi[[All,1]]^Sort[ fi[ [All,2]]])]; Array[fise,100] (* Harvey P. Dale, Sep 18 2017 *)

a(n) >= n. - Michel Marcus, Jul 30 2015

Corrected and extended by Ray Chandler, Aug 17 2003

A087315 a(n) = Product_{k=1..n} prime(k)^prime(n-k+1).

Original entry on oeis.org

1, 4, 72, 21600, 190512000, 580909190400000, 428616352408083840000000, 859278392084450410309036800000000000, 2097197194438629126172451944256706311040000000000000

Offset: 0

Amarnath Murthy, Sep 03 2003

nonn

			a(3) = 2^5*3^3*5^2 = 21600.

G. C. Greubel, Table of n, a(n) for n = 0..23

Cf. A006939, A002110, A025487, A004394, A002093, A002182, A055932, A025487, A089247, A071364, A097320, A046523, A056166, A114129, A053810.

[1] cat [(&*[NthPrime(k)^(NthPrime(n-k+1)): k in [1..n]]): n in [1..10]]; // G. C. Greubel, Oct 14 2018

seq(product(ithprime(k)^ithprime(n-k+1), k=1..n), n=0..10);

Table[Product[Prime[k]^Prime[n - k + 1], {k, 1, n}], {n, 0, 10}] (* G. C. Greubel, Oct 14 2018 *)

for(n=0, 10, print1(prod(k=1,n, prime(k)^prime(n-k+1)), ", ")) \\ G. C. Greubel, Oct 14 2018

[prod(nth_prime(i)^nth_prime(k-i+1) for i in (1..k)) for k in (0..10)] # Giuseppe Coppoletta, Nov 03 2014

More terms from Jorge Coveiro, Dec 22 2004

Corrected by David Wasserman, May 02 2005

A089247 a(n) = smallest number obtainable by permuting the exponents in the prime factorization of n.

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 12, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 20, 51, 52, 53, 24, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72

Offset: 1

Sam Alexander, Dec 11 2003

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Cf. A027748, A124010, A046523, A071364, A085079.

import Data.List (sort)
a089247 n = product $ zipWith (^)
                      (a027748_row n) (reverse $ sort $ a124010_row n)
-- Reinhard Zumkeller, Apr 27 2013

a(n)=my(f=factor(n)); f[,2]=vecsort(f[,2],,4); factorback(f) \\ Charles R Greathouse IV, Sep 02 2015

A334032 The a(n)-th composition in standard order (graded reverse-lexicographic) is the unsorted prime signature of n.

Original entry on oeis.org

0, 1, 1, 2, 1, 3, 1, 4, 2, 3, 1, 5, 1, 3, 3, 8, 1, 6, 1, 5, 3, 3, 1, 9, 2, 3, 4, 5, 1, 7, 1, 16, 3, 3, 3, 10, 1, 3, 3, 9, 1, 7, 1, 5, 5, 3, 1, 17, 2, 6, 3, 5, 1, 12, 3, 9, 3, 3, 1, 11, 1, 3, 5, 32, 3, 7, 1, 5, 3, 7, 1, 18, 1, 3, 6, 5, 3, 7, 1, 17, 8, 3, 1, 11

Offset: 1

Gus Wiseman, Apr 17 2020

nonn

Unsorted prime signature (A124010) is the sequence of exponents in a number's prime factorization.

The k-th composition in standard order (row k of A066099) is obtained by taking the set of positions of 1's in the reversed binary expansion of k, prepending 0, taking first differences, and reversing again. This gives a bijective correspondence between nonnegative integers and integer compositions.

			The unsorted prime signature of 12345678 is (1,2,1,1), which is the 27th composition in standard order, so a(12345678) = 27.

Positions of first appearances are A057335 (a partial inverse).
Least number with same prime signature is A071364.
Unsorted prime signature is A124010.
Least number with reversed prime signature is A331580.
Minimal numbers with standard reversed prime signatures are A334031.
The reversed version is A334033.
All of the following pertain to compositions in standard order (A066099):
- Length is A000120.
- Sum is A070939.
- Strict compositions are A233564.
- Constant compositions are A272919.
- Aperiodic compositions are A328594.
- Normal compositions are A333217.
- Permutations are A333218.
- Heinz number is A333219.
Cf. A029931, A048793, A052409, A055932, A056239, A112798, A124767, A228351, A233249, A329139, A333220.

stcinv[q_]:=Total[2^Accumulate[Reverse[q]]]/2;
Table[stcinv[Last/@If[n==1,{},FactorInteger[n]]],{n,100}]

a(A057335(n)) = n.
A057335(a(n)) = A071364(n).
a(A334031(n))= A059893(n).
A334031(a(n)) = A331580(n).

A083256 a(n) = A046523(n-th nonprime number) = A046523(A018252(n)).

Original entry on oeis.org

1, 4, 6, 8, 4, 6, 12, 6, 6, 16, 12, 12, 6, 6, 24, 4, 6, 8, 12, 30, 32, 6, 6, 6, 36, 6, 6, 24, 30, 12, 12, 6, 48, 4, 12, 6, 12, 24, 6, 24, 6, 6, 60, 6, 12, 64, 6, 30, 12, 6, 30, 72, 6, 12, 12, 6, 30, 48, 16, 6, 60, 6, 6, 6, 24, 60, 6, 12, 6, 6, 6, 96, 12, 12, 36, 30, 24, 30, 6, 72, 30, 6, 48

Offset: 1

Labos Elemer, May 09 2003

nonn

Amiram Eldar, Table of n, a(n) for n = 1..10000

Cf. A007395, A000040, A002808, A018252, A046523, A071364, A083257.

f[n_] := Module[{e = ReverseSort[FactorInteger[n][[;; , 2]]]}, Times @@ (Prime[Range[Length[e]]]^e)]; f[1] = 1; f /@ Select[Range[120], !PrimeQ[#] &] (* Amiram Eldar, Feb 22 2025 *)

Corrected by Ray Chandler, Aug 01 2004

A329607 a(n) = A007947(A122111(n)).

Original entry on oeis.org

1, 2, 2, 3, 2, 6, 2, 5, 3, 6, 2, 10, 2, 6, 6, 7, 2, 15, 2, 10, 6, 6, 2, 14, 3, 6, 5, 10, 2, 30, 2, 11, 6, 6, 6, 21, 2, 6, 6, 14, 2, 30, 2, 10, 10, 6, 2, 22, 3, 15, 6, 10, 2, 35, 6, 14, 6, 6, 2, 42, 2, 6, 10, 13, 6, 30, 2, 10, 6, 30, 2, 33, 2, 6, 15, 10, 6, 30, 2, 22, 7, 6, 2, 42, 6, 6, 6, 14, 2, 70, 6, 10, 6, 6, 6, 26, 2, 15, 10, 21, 2, 30, 2, 14, 30

Offset: 1

Antti Karttunen, Nov 17 2019

nonn

Antti Karttunen, Table of n, a(n) for n = 1..65537
Index entries for sequences computed from indices in prime factorization

Cf. A007947, A064989, A071364, A077462, A108951, A122111, A181819, A181821, A329600.

Block[{f}, f[1] = 1; f[n_] := Module[{l = #, m = 0}, Times @@ Power @@@ Table[l -= m; l = DeleteCases[l, 0]; {Prime@ Length@ l, m = Min@ l}, Length@ Union@ l]] &@ Catenate[ConstantArray[PrimePi[#1], #2] & @@@ FactorInteger@ n]; Array[If[# < 1, 0, Sum[EulerPhi[d] Abs@ MoebiusMu[d], {d, Divisors[#]}]] &@ f[#] &, 105]] (* Michael De Vlieger, Nov 18 2019, after JungHwan Min at A122111. *)

A007947(n) = factorback(factorint(n)[, 1]);
A064989(n) = {my(f); f = factor(n); if((n>1 && f[1,1]==2), f[1,2] = 0); for (i=1, #f~, f[i,1] = precprime(f[i,1]-1)); factorback(f)};
A122111(n) = if(1==n,n,prime(bigomega(n))*A122111(A064989(n)));
A329607(n) = A007947(A122111(n));

a(n) = A007947(A122111(n)) = A007947(A181819(A108951(n))).
a(n) = A122111(A071364(n)).
A181821(a(n)) = A329600(n).

cp's OEIS Frontend

A336835 Number of iterations of x -> A003961(x) needed before the result is deficient (sigma(x) < 2x), when starting from x=n.

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A077462 Prime factor configuration patterns.

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A336389 The least positive integer k for which A336835(k) >= n, where A336835(k) is the number of iterations of x -> A003961(x) needed before the result is deficient (sigma(x) < 2x), when starting from x=k.

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A329600 Smallest number with the same set of distinct prime exponents as A108951(n).

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A085079 Largest number with the prime signature of n using prime divisors of n.

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A087315 a(n) = Product_{k=1..n} prime(k)^prime(n-k+1).

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A089247 a(n) = smallest number obtainable by permuting the exponents in the prime factorization of n.

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