A014197 -id:A014197 - cp's OEIS frontend

A131934 Records in A014197.

2, 3, 4, 5, 6, 10, 11, 17, 21, 31, 34, 37, 38, 49, 54, 72, 98, 126, 129, 176, 178, 247, 276, 281, 331, 359, 399, 441, 454, 525, 558, 692, 718, 734, 764, 1023, 1138, 1485, 1755, 2008, 2166, 2590, 2702, 2733, 3169, 3687, 3802, 4133, 4604, 5025, 5841, 6019, 6311

Offset: 1

N. J. A. Sloane, Nov 05 2007

nonn

Jud McCranie, Table of n, a(n) for n = 1..109 (terms 1..79 from T. D. Noe, terms 80..86 from Donovan Johnson)

Cf. A000010, A014197, A097942.

# For the function HighlyTotientNumbers see A097942.
A131934_list := n -> seq(s[2], s = HighlyTotientNumbers(n));
A131934_list(500); # Peter Luschny, Sep 01 2012

# For the function HighlyTotientNumbers see A097942.
A131934_list = lambda n: [s[1] for s in HighlyTotientNumbers(n)]
A131934_list(500) # Peter Luschny, Sep 01 2012

a(n) = A014197(A097942(n)). - R. J. Mathar, Nov 07 2007

More terms from R. J. Mathar, Nov 07 2007
Deleted my csh program which is unstable at high indices - R. J. Mathar, Mar 17 2010
Corrected and extended by T. D. Noe, Mar 16 2010

A305896 Filter sequence combining prime signature of n (A046523) and the cardinality of invphi (A014197).

Original entry on oeis.org

1, 2, 3, 4, 3, 5, 3, 6, 7, 8, 3, 9, 3, 10, 10, 11, 3, 12, 3, 13, 10, 8, 3, 14, 7, 10, 15, 16, 3, 17, 3, 18, 10, 10, 10, 19, 3, 10, 10, 20, 3, 21, 3, 22, 23, 8, 3, 24, 7, 23, 10, 16, 3, 25, 10, 26, 10, 8, 3, 27, 3, 10, 23, 28, 10, 17, 3, 23, 10, 17, 3, 29, 3, 10, 23, 23, 10, 17, 3, 30, 31, 8, 3, 32, 10, 10, 10, 33, 3, 34, 10, 22, 10, 10, 10, 35, 3, 23, 23, 36

Offset: 1

Antti Karttunen, Jul 01 2018

nonn

Restricted growth sequence transform of ordered pair [A046523(n), A014197(n)].

For all i, j: A305801(i) = A305801(j) => a(i) = a(j) => A097946(i) = A097946(j).

Antti Karttunen, Table of n, a(n) for n = 1..65537

Cf. A014197, A046523, A305801.

Cf. also A097946.

up_to = 65537;
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; };
A014197(n, m=1) = { n==1 && return(1+(m<2)); my(p, q); sumdiv(n, d, if( d>=m && isprime(d+1), sum( i=0, valuation(q=n\d, p=d+1), A014197(q\p^i, p))))} \\ This function from M. F. Hasler, Oct 05 2009
A046523(n) = { my(f=vecsort(factor(n)[, 2], , 4), p); prod(i=1, #f, (p=nextprime(p+1))^f[i]); };  \\ From A046523
Aux305896(n) = [A046523(n), A014197(n)];
v305896 = rgs_transform(vector(up_to, n, Aux305896(n)));
A305896(n) = v305896[n];

A097946 a(n) = A008683(n)*A014197(n) where A008683 is the Moebius (or Mobius) function mu(n) and A014197 is the number of numbers m with Euler phi(m) = n.

Original entry on oeis.org

2, -3, 0, 0, 0, 4, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, -2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -4, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, -2, 0, 0, 0, -2, 0, 0, 0, 0, 0, 0, 0, -2, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

Offset: 1

Gerald McGarvey, Sep 04 2004

sign

For n < 93 and a(n) not 0, n = p - 1 where p is prime and therefore in A077064 (Squarefree numbers of form prime - 1.)

Antti Karttunen, Table of n, a(n) for n = 1..10000

Cf. A000010, A008683, A014197, A077064, A097945.

A014197(n, m=1) = { n==1 && return(1+(m<2)); my(p, q); sumdiv(n, d, if( d>=m && isprime(d+1), sum( i=0, valuation(q=n\d, p=d+1), A014197(q\p^i, p))))} \\ This function from M. F. Hasler, Oct 05 2009
A097946(n) = moebius(n)*A014197(n); \\ Antti Karttunen, Jul 19 2017

A322019 a(n) = A000005(n) - A014197(n), where A000005(n) gives the number of divisors of n, and A014197(n) gives the number of integers m with phi(m) = n.

Original entry on oeis.org

-1, -1, 2, -1, 2, 0, 2, -1, 3, 2, 2, 0, 2, 4, 4, -1, 2, 2, 2, 1, 4, 2, 2, -2, 3, 4, 4, 4, 2, 6, 2, -1, 4, 4, 4, 1, 2, 4, 4, -1, 2, 4, 2, 3, 6, 2, 2, -1, 3, 6, 4, 4, 2, 6, 4, 5, 4, 2, 2, 3, 2, 4, 6, -1, 4, 6, 2, 6, 4, 6, 2, -5, 2, 4, 6, 6, 4, 6, 2, 0, 5, 2, 2, 6, 4, 4, 4, 2, 2, 12, 4, 3, 4, 4, 4, -5, 2, 6, 6, 5, 2, 6, 2, 5, 8

Offset: 1

Antti Karttunen, Dec 03 2018

sign

Antti Karttunen, Table of n, a(n) for n = 1..20790
Antti Karttunen, Data supplement: n, a(n) computed for n = 1..100000

Cf. A000005, A014197, A305058 (positions of zeros).

Cf. also A305896.

A014197(n, m=1) = { n==1 && return(1+(m<2)); my(p, q); sumdiv(n, d, if( d>=m && isprime(d+1), sum( i=0, valuation(q=n\d, p=d+1), A014197(q\p^i, p))))}; \\ From A014197
A322019(n) = (numdiv(n)-A014197(n));

a(n) = A000005(n) - A014197(n).

A322024 Lexicographically earliest such sequence a that a(i) = a(j) => A014197(i) = A014197(j) and A081373(i) = A081373(j), for all i, j. Here A081373(n) gives the number of k, 1 <= k <= n, with phi(k) = phi(n), while A014197(n) gives the number of integers m with phi(m) = n.

Original entry on oeis.org

1, 2, 3, 4, 3, 5, 3, 6, 7, 8, 3, 9, 3, 10, 3, 11, 3, 12, 3, 13, 7, 14, 3, 15, 3, 10, 7, 16, 3, 17, 3, 18, 7, 10, 3, 19, 3, 10, 7, 20, 3, 21, 3, 22, 10, 14, 3, 23, 7, 24, 3, 16, 3, 16, 7, 25, 7, 14, 3, 26, 3, 7, 10, 27, 3, 17, 3, 10, 3, 28, 3, 29, 3, 24, 10, 30, 7, 31, 3, 15, 3, 16, 3, 32, 3, 10, 3, 33, 3, 34, 7, 2, 10, 7, 10, 35, 3, 24, 24, 21, 3, 28, 3, 2, 10

Offset: 1

Antti Karttunen, Nov 29 2018

nonn

Restricted growth sequence transform of the ordered pair [A014197(n), A081373(n)].

Antti Karttunen, Table of n, a(n) for n = 1..65537

Cf. A014197, A081373, A305896, A319339, A322023.

up_to = 65537;
ordinal_transform(invec) = { my(om = Map(), outvec = vector(length(invec)), pt); for(i=1, length(invec), if(mapisdefined(om,invec[i]), pt = mapget(om, invec[i]), pt = 0); outvec[i] = (1+pt); mapput(om,invec[i],(1+pt))); outvec; };
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; };
A014197(n, m=1) = { n==1 && return(1+(m<2)); my(p, q); sumdiv(n, d, if( d>=m && isprime(d+1), sum( i=0, valuation(q=n\d, p=d+1), A014197(q\p^i, p))))}; \\ From A014197
v081373 = ordinal_transform(vector(up_to,n,eulerphi(n)));
A081373(n) = v081373[n];
v322024 = rgs_transform(vector(up_to, n, [A014197(n), A081373(n)]));
A322024(n) = v322024[n];

A347524 E.g.f.: exp(Sum_{k>=1} A014197(k)*x^k).

Original entry on oeis.org

1, 2, 10, 44, 364, 2552, 28504, 267920, 3762448, 44426528, 733803424, 10281376448, 197599119040, 3231560909696, 69960323019136, 1295278340380928, 31334430312038656, 650842176105505280, 17337350481203210752, 397746862137852603392, 11579274068100022660096

Offset: 0

Vaclav Kotesovec, Sep 05 2021

nonn

Vaclav Kotesovec, Table of n, a(n) for n = 0..400

Cf. A000010, A014197, A120963, A280611.

E.g.f.: exp(Sum_{k>=1} x^A000010(k)).

log(a(n)/n!) ~ 3*sqrt(70*zeta(3)*n)/Pi^2.

A005277 Nontotients: even numbers k such that phi(m) = k has no solution.

Original entry on oeis.org

14, 26, 34, 38, 50, 62, 68, 74, 76, 86, 90, 94, 98, 114, 118, 122, 124, 134, 142, 146, 152, 154, 158, 170, 174, 182, 186, 188, 194, 202, 206, 214, 218, 230, 234, 236, 242, 244, 246, 248, 254, 258, 266, 274, 278, 284, 286, 290, 298, 302, 304, 308, 314, 318

Offset: 1

N. J. A. Sloane

nonn

If p is prime then the following two statements are true. I. 2p is in the sequence iff 2p+1 is composite (p is not a Sophie Germain prime). II. 4p is in the sequence iff 2p+1 and 4p+1 are composite. - Farideh Firoozbakht, Dec 30 2005
Another subset of nontotients consists of the numbers j^2 + 1 such that j^2 + 2 is composite. These numbers j are given in A106571. Similarly, let b be 3 or a number such that b == 1 (mod 4). For any j > 0 such that b^j + 2 is composite, b^j + 1 is a nontotient. - T. D. Noe, Sep 13 2007
The Firoozbakht comment can be generalized: Observe that if k is a nontotient and 2k+1 is composite, then 2k is also a nontotient. See A057192 and A076336 for a connection to Sierpiński numbers. This shows that 271129*2^j is a nontotient for all j > 0. - T. D. Noe, Sep 13 2007

			There are no values of m such that phi(m)=14, so 14 is a term of the sequence.

Albert H. Beiler, Recreations in the theory of numbers, New York, Dover, (2nd ed.) 1966. See Table 44 at p. 91.
R. K. Guy, Unsolved Problems in Number Theory, B36.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
David Wells, The Penguin Dictionary of Curious and Interesting Numbers. Penguin Books, NY, 1986, Revised edition 1987. See p. 91.

Robert G. Wilson v, Table of n, a(n) for n = 1..29750 (terms 1..10000 from T. D. Noe).
Lambert A'Campo, Every 7-Dimensional Abelian Variety over the p-adic Numbers has a Reducible L-adic Galois Representation, arXiv:2006.06737 [math.NT], 2020.
Matteo Caorsi and Sergio Cecotti, Geometric classification of 4d N=2 SCFTs, arXiv:1801.04542 [hep-th], 2018.
K. Ford, S. Konyagin, and C. Pomerance, Residue classes free of values of Euler's function, arXiv:2005.01078 [math.NT] (1999).
L. Havelock, A Few Observations on Totient and Cototient Valence.
Eric Weisstein's World of Mathematics, Nontotient.
Wikipedia, Nontotient.
Robert G. Wilson v, Letter to N. J. A. Sloane, Jul. 1992.

See A007617 for all numbers k (odd or even) such that phi(m) = k has no solution.
All even numbers not in A002202. Cf. A000010.
Cf. A005384, A006093, A014197, A057192, A076336, A079695, A106571.

a005277 n = a005277_list !! (n-1)
a005277_list = filter even a007617_list
-- Reinhard Zumkeller, Nov 22 2015

[n: n in [2..400 by 2] | #EulerPhiInverse(n) eq 0]; // Marius A. Burtea, Sep 08 2019

A005277 := n -> if type(n,even) and invphi(n)=[] then n fi: seq(A005277(i),i=1..318); # Peter Luschny, Jun 26 2011

searchMax = 320; phiAnsYldList = Table[0, {searchMax}]; Do[phiAns = EulerPhi[m]; If[phiAns <= searchMax, phiAnsYldList[[phiAns]]++ ], {m, 1, searchMax^2}]; Select[Range[searchMax], EvenQ[ # ] && (phiAnsYldList[[ # ]] == 0) &] (* Alonso del Arte, Sep 07 2004 *)
totientQ[m_] := Select[ Range[m +1, 2m*Product[(1 - 1/(k*Log[k]))^(-1), {k, 2, DivisorSigma[0, m]}]], EulerPhi[#] == m &, 1] != {}; (* after Jean-François Alcover, May 23 2011 in A002202 *) Select[2 Range@160, ! totientQ@# &] (* Robert G. Wilson v, Mar 20 2023 *)

is(n)=n%2==0 && !istotient(n) \\ Charles R Greathouse IV, Mar 04 2017

a(n) = 2*A079695(n). - R. J. Mathar, Sep 29 2021

{k: k even and A014197(k) = 0}. - R. J. Mathar, Sep 29 2021

More terms from Jud McCranie, Oct 13 2000

A082695 Decimal expansion of zeta(2)*zeta(3)/zeta(6).

Original entry on oeis.org

1, 9, 4, 3, 5, 9, 6, 4, 3, 6, 8, 2, 0, 7, 5, 9, 2, 0, 5, 0, 5, 7, 0, 7, 0, 3, 6, 2, 5, 7, 4, 7, 6, 3, 4, 3, 7, 1, 8, 7, 8, 5, 8, 5, 0, 1, 7, 6, 7, 8, 0, 5, 7, 1, 6, 0, 2, 6, 6, 3, 5, 6, 8, 8, 9, 0, 0, 5, 3, 4, 9, 5, 0, 6, 9, 3, 5, 5, 4, 0, 5, 3, 9, 4, 8, 1, 7, 9, 1, 0, 0, 8, 2, 1, 1, 1, 1, 3, 0, 1, 0, 6, 9, 0, 5

Offset: 1

Benoit Cloitre, Apr 12 2003

Equals the Dirichlet zeta-function Sum_{n>=1} A001615(n)/n^s at s=3. - R. J. Mathar, Apr 02 2011
Dressler shows that this is the average value of A014197, that is, the number of values m such that phi(m) <= n is asymptotically n times this constant. Erdős had shown earlier that this limit exists. - Charles R Greathouse IV, Nov 26 2013
From Stanislav Sykora, Nov 14 2014: (Start)
Equals lim_{n->infinity} (Sum_{k=1..n} k/phi(k))/n, i.e., the limit mean value of k/phi(k), where phi(k) is Euler's totient function.
Also equals lim_{n->infinity} (Sum_{k=1..n} 1/phi(k))/log(n).
Proofs are trivial using the formulas for Sum_{k=1..n} k/phi(k) and Sum_{k=1..n} 1/phi(k) listed in the Wikipedia link.
For the limit mean value of phi(k)/k, see A059956. (End)
The asymptotic mean of A005361. - Amiram Eldar, Apr 13 2020

			1.94359643682075920505707036257476343718785850176780571602663568890 ...

Steven R. Finch, Mathematical Constants, Encyclopedia of Mathematics and its Applications, vol. 94, Cambridge University Press, 2003, Section 2.7, p. 116.
Joe Roberts, Lure of the Integers, Mathematical Association of America, 1992. See p. 74.

Stanislav Sykora, Table of n, a(n) for n = 1..2000
Paul T. Bateman, The distribution of values of the Euler function, Acta Arithmetica 21:1 (1972), pp. 329-345.
Olivier Bordellès and Benoit Cloitre, An Alternating Sum Involving the Reciprocal of Certain Multiplicative Functions, J. Int. Seq. 16 (2013) #13.6.3.
Robert E. Dressler, A density which counts multiplicity, Pacific J. Math. 34 (1970), pp. 371-378.
Paul Erdős, Some remarks on Euler's ϕ function and some related problems, Bull. Amer. Math. Soc. 51 (1945), pp. 540-544.
J. von zur Gathen et al., Average order in cyclic groups, J. Theor. Nombres Bordeaux, 16 (2004), 107-123. Lists several other papers where this constant arises.
S. W. Golomb, Powerful numbers, Amer. Math. Monthly, Vol. 77 (1970), 848-852.
D. Handelman, Invariants for critical dimension groups and permutation-Hermite equivalence, arXiv preprint arXiv:1309.7417 [math.AC], 2013.
Eric Weisstein's World of Mathematics, Totient Summatory Function.
Eric Weisstein's World of Mathematics, Powerful Number.
Wikipedia, Euler's totient function.

Cf. A000010, A001615, A001694, A002117, A005117, A005361, A013661, A013664, A014197, A059956, A068468, A070243, A082696 (continued fraction), A157292.

First@RealDigits[ Zeta[2]*Zeta[3]/Zeta[6], 10, 100]
RealDigits[ 315 Zeta[3]/(2 Pi^4), 10, 111][[1]] (* Robert G. Wilson v, Aug 11 2014 *)

PARI
```
zeta(3)*315/2/Pi^4
```

Decimal expansion of Product_{p prime} (1+1/p/(p-1)) = zeta(2)*zeta(3)/zeta(6) = 1.94359643682075920505707...
The sum of the reciprocals of the powerful numbers, A001694. - T. D. Noe, May 03 2006
Equals A013661 * A002117 / A013664 = 1 / A068468 = zeta(3) * 315/(2*Pi^4) = zeta(3) * A157292.
Equals Sum_{k>=1} mu(k)^2/(k*phi(k)) (the sum of reciprocals of the squarefree numbers multiplied by their Euler totient function values, A000010). - Amiram Eldar, Aug 18 2020

New definition from Eric W. Weisstein, May 04 2006

A057635 a(n) is the largest m such that phi(m) = n, where phi is Euler's totient function = A000010, or a(n) = 0 if no such m exists.

Original entry on oeis.org

2, 6, 0, 12, 0, 18, 0, 30, 0, 22, 0, 42, 0, 0, 0, 60, 0, 54, 0, 66, 0, 46, 0, 90, 0, 0, 0, 58, 0, 62, 0, 120, 0, 0, 0, 126, 0, 0, 0, 150, 0, 98, 0, 138, 0, 94, 0, 210, 0, 0, 0, 106, 0, 162, 0, 174, 0, 118, 0, 198, 0, 0, 0, 240, 0, 134, 0, 0, 0, 142, 0, 270, 0, 0, 0, 0, 0, 158, 0, 330, 0

Offset: 1

Jud McCranie, Oct 10 2000

nonn

To check that a property P holds for all EulerPhi(x) not exceeding n, for n with a(n) > 0, it suffices to check P for all EulerPhi(x) with x not exceeding a(n). - Joseph L. Pe, Jan 10 2002
The Alekseyev link in A131883 establishes the following explicit relationship between A131883, A036912 and A057635: for t belonging to A036912, we have t = A131883(A057635(t)-1). In other words, A036912(n) = A131883(A057635(A036912(n))-1) for all n.
From Jianing Song, Feb 16 2019: (Start)
Let f(n) = exp(gamma)*log(log(n)) + 2.5/log(log(n)), then a(n) < n*f(n^2) for all n > 1, where gamma = A001620.
Proof. Without loss of generality we suppose log(log(n)) > n_0 = sqrt(2.5/exp(gamma)) = 1.18475..., then f(n), n/f(n) and N(n) = ceiling(n*f(n^2)) are all monotonically increasing functions of n, and we have f(n) < 2*exp(gamma)*log(log(n)).
By the formula (3.41) in Theorem 15 by J. Barkley Rosser and Lowell Schoenfeld we have phi(k) > k/f(k) for k != 1, 2, 223092870. N(31802157) = 223092869 < 223092870, N(31802158) = 223092877 > 223092870, so N(n) != 223092870 (N(n) is increasing). So phi(N(n)) > N(n)/f(N(n)) > (n*f(n^2))/f(n*f(n^2)) (n/f(n) is increasing and log(log(n*f(n^2))) > n_0).
Note that f(n^2) < 2*exp(gamma)*log(log(n^2)) < 2*exp(gamma)*(log(n^2)/e) = 4*exp(gamma-1)*log(n) < 4*exp(gamma-2)*n < n, so n*f(n^2) < n^2, f(n*f(n^2)) < f(n^2) (f(n) is increasing and log(log(n*f(n^2))) > n_0), so phi(N(n)) > n. As a result, a(n) <= N(n) - 1 < n*f(n^2).
Conjecturally a(n) < n*f(n) for all n > 2. (End)

			m = 12 is the largest value of m such that phi(m) = 4, so a(4) = 12.

T. D. Noe, Table of n, a(n) for n = 1..10000
Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).
J. Barkley Rosser and Lowell Schoenfeld, Approximate formulas for some functions of prime numbers, Illinois J. Math. 6 (1) (1962), 64-94.

Cf. A000010, A005277, A014197, A049283.

Cf. A006511 (largest k for which A000010(k) = A002202(n)).

a = Table[0, {100}]; Do[ t = EulerPhi[n]; If[t < 101, a[[t]] = n], {n, 1, 10^6}]; a

a(n) = if(n%2, 2*(n==1), forstep(k=floor(exp(Euler)*n*log(log(n^2))+2.5*n/log(log(n^2))), n, -1, if(eulerphi(k)==n, return(k)); if(k==n, return(0)))) \\ Jianing Song, Feb 15 2019

apply( {A057635(n,m=istotient(n))=if(!m, 0, n>1, m=log(log(n)*2); m=bitand(n*(exp(Euler)*m+2.5/m)\1,-2); while(eulerphi(m)!=n, m-=2); m, 2)}, [1..99]) \\ If n is known to be a totient, a nonzero 2nd arg can be given to avoid the check. - M. F. Hasler, Aug 13 2021

a(n) = invphiMax(n); \\ Amiram Eldar, Nov 14 2024 using Max Alekseyev's invphi.gp

a(2n+1) = 0 for n > 0, and a(2n) = 0 iff 2n is in A005277.

Edited and escape clause added to definition by M. F. Hasler, Aug 13 2021

A058277 Number of values of k such that phi(k) = n, where n runs through the values (A002202) taken by phi.

Original entry on oeis.org

2, 3, 4, 4, 5, 2, 6, 6, 4, 5, 2, 10, 2, 2, 7, 8, 9, 4, 3, 2, 11, 2, 2, 3, 2, 9, 8, 2, 2, 17, 2, 10, 2, 6, 6, 3, 17, 4, 2, 3, 2, 9, 2, 6, 3, 17, 2, 9, 2, 7, 2, 2, 3, 21, 2, 2, 7, 12, 4, 3, 2, 12, 2, 8, 2, 10, 4, 2, 21, 2, 2, 8, 3, 4, 2, 3, 19, 5, 2, 8, 2, 2, 6, 2, 31, 2, 9, 10

Offset: 1

Claude Lenormand (claude.lenormand(AT)free.fr), Jan 05 2001

Carmichael (1922) conjectured that the number 1 never appears in this sequence. Sierpiński conjectured and Ford (1998) proved that all integers greater than 1 occur in the sequence. Erdős (1958) proved that if s >= 1 appears in the sequence then it appears infinitely often. - Nick Hobson, Nov 04 2006

A002202(n) occurs a(n) times in A007614. - Reinhard Zumkeller, Nov 22 2015

Édouard Lucas, Théorie des Nombres, Blanchard 1958.

T. D. Noe, Table of n, a(n) for n=1..10000
Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).
R. D. Carmichael, Note on Euler's totient function, Bull. Amer. Math. Soc. 28 (1922), pp. 109-110.
Paul Erdős, Some remarks on Euler's totient function, Acta Arith. 4 (1958), pp. 10-19.
M. Farrokhi D. G., Gap function to compute the inverse of Euler's totient function.
Kevin Ford, The distribution of totients, Electron. Res. Announc. Amer. Math. Soc. 4 (1998), 27-34.
Nick Hobson, Solution to puzzle 152: Totient valence.
Eric Weisstein's World of Mathematics, Totient Valence Function.

The nonzero terms of A014197.
Cf. A000010, A002202, A007614.
Cf. A006511 (largest k for which A000010(k) = A002202(n)).

import Data.List (group)
a058277 n = a058277_list !! (n-1)
a058277_list = map length $ group a007614_list
-- Reinhard Zumkeller, Nov 22 2015

max = 300; inversePhi[?OddQ] = {}; inversePhi[1] = {1, 2}; inversePhi[m] := Module[{p, nmax, n, nn}, p = Select[Divisors[m] + 1, PrimeQ]; nmax = m * Times @@ (p/(p-1)); n = m; nn = Reap[While[n <= nmax, If[EulerPhi[n] == m, Sow[n]]; n++]] // Last; If[nn == {}, {}, First[nn] ] ]; Reap[For[n = 1, n <= max, n = If[n == 1, 2, n+2], nn = inversePhi[n] ; If[nn != {} , Sow[nn // Length] ] ] ] // Last // First (* Jean-François Alcover, Nov 21 2013 *)

lista(nmax) = {my(m); for(n = 1, nmax, m = invphiNum(n); if(m > 0, print1(m, ", ")));} \\ Amiram Eldar, Nov 15 2024 using Max Alekseyev's invphi.gp

More terms from Nick Hobson, Nov 04 2006

cp's OEIS Frontend

A131934 Records in A014197.

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A305896 Filter sequence combining prime signature of n (A046523) and the cardinality of invphi (A014197).

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A097946 a(n) = A008683(n)*A014197(n) where A008683 is the Moebius (or Mobius) function mu(n) and A014197 is the number of numbers m with Euler phi(m) = n.

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A322019 a(n) = A000005(n) - A014197(n), where A000005(n) gives the number of divisors of n, and A014197(n) gives the number of integers m with phi(m) = n.

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A322024 Lexicographically earliest such sequence a that a(i) = a(j) => A014197(i) = A014197(j) and A081373(i) = A081373(j), for all i, j. Here A081373(n) gives the number of k, 1 <= k <= n, with phi(k) = phi(n), while A014197(n) gives the number of integers m with phi(m) = n.

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A347524 E.g.f.: exp(Sum_{k>=1} A014197(k)*x^k).

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A005277 Nontotients: even numbers k such that phi(m) = k has no solution.

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A082695 Decimal expansion of zeta(2)*zeta(3)/zeta(6).

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