A004257 -id:A004257 - cp's OEIS frontend

A002064 Cullen numbers: a(n) = n*2^n + 1.

1, 3, 9, 25, 65, 161, 385, 897, 2049, 4609, 10241, 22529, 49153, 106497, 229377, 491521, 1048577, 2228225, 4718593, 9961473, 20971521, 44040193, 92274689, 192937985, 402653185, 838860801, 1744830465, 3623878657, 7516192769, 15569256449, 32212254721, 66571993089

Offset: 0

N. J. A. Sloane

Binomial transform is A084859. Inverse binomial transform is A004277. - Paul Barry, Jun 12 2003
Let A be the Hessenberg matrix of order n defined by: A[1,j]=1, A[i,i]:=2,(i>1), A[i,i-1] =-1, and A[i,j]=0 otherwise. Then, for n>=1, a(n-1)= (-1)^(n-1)*coeff(charpoly(A,x),x). - Milan Janjic, Jan 26 2010
Indices of primes are listed in A005849. - M. F. Hasler, Jan 18 2015
Add the list of fractions beginning with 1/2 + 3/4 + 7/8 + ... + (2^n - 1)/2^n and take the sums pairwise from left to right. For 1/2 + 3/4 = 5/4, 5 + 4 = 9 = a(2); for 5/4 + 7/8 = 17/8, 17 + 8 = 25 = a(3); for 17/8 + 15/16 = 49/16, 49 + 16 = 65 = a(4); for 49/16 + 31/32 = 129/32, 129 + 32 = 161 = a(5). For each pairwise sum a/b, a + b = n*2^(n+1). - J. M. Bergot, May 06 2015
Number of divisors of (2^n)^(2^n). - Gus Wiseman, May 03 2021
Named after the Irish Jesuit priest James Cullen (1867-1933), who checked the primality of the terms up to n=100. - Amiram Eldar, Jun 05 2021

			G.f. = 1 + 3*x + 9*x^2 + 25*x^3 + 65*x^4 + 161*x^5 + 385*x^6 + 897*x^7 + ... - _Michael Somos_, Jul 18 2018

G. Everest, A. van der Poorten, I. Shparlinski and T. Ward, Recurrence Sequences, Amer. Math. Soc., 2003; see esp. p. 255.
R. K. Guy, Unsolved Problems in Number Theory, B20.
Paulo Ribenboim, The Little Book of Bigger Primes, Springer-Verlag NY 2004. See pp. 240-242.
W. Sierpiński, Elementary Theory of Numbers. Państ. Wydaw. Nauk., Warsaw, 1964, p. 346.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

T. D. Noe, Table of n, a(n) for n=0..300
Ray Ballinger, Cullen Primes: Definition and Status.
Attila Bérczes, István Pink, and Paul Thomas Young, Cullen numbers and Woodall numbers in generalized Fibonacci sequences, J. Num. Theor. (2024) Vol. 262, 86-102.
Yuri Bilu, Diego Marques, and Alain Togbé, Generalized Cullen numbers in linear recurrence sequences, Journal of Number Theory, Vol. 202 (2019), pp. 412-425; arXiv preprint, arXiv:1806.09441 [math.NT], 2018.
Daniel Birmajer, Juan B. Gil, David S. Kenepp, and Michael D. Weiner, Restricted generating trees for weak orderings, arXiv:2108.04302 [math.CO], 2021.
C. K. Caldwell, The Top Twenty: Cullen Primes.
James Cullen, Question 15897, Educational Times, Vol. 58 (December 1905), p. 534.
Orhan Eren and Yüksel Soykan, Gaussian Generalized Woodall Numbers, Arch. Current Res. Int'l (2023) Vol. 23, Iss. 8, Art. No. ACRI.108618, 48-68. See p. 50.
Orhan Eren and Yüksel Soykan, On Dual Hyperbolic Generalized Woodall Numbers, Archives Current Res. Int'l (2024) Vol. 24, Iss. 11, Art. No. ACRI.126420, 398-423. See p. 401.
Jon Grantham and Hester Graves, The abc Conjecture Implies That Only Finitely Many Cullen Numbers Are Repunits, arXiv:2009.04052 [math.NT], 2020.
José María Grau and Florian Luca, Cullen numbers with the Lehmer property, Proceedings of the American Mathematical Society, Vol. 140, No. 1 (2012), pp. 129-134; arXiv preprint, arXiv:1103.3578 [math.NT], Mar 18 2011.
Paul Leyland, Factors of Cullen and Woodall numbers.
Paul Leyland, Generalized Cullen and Woodall numbers.
Diego Marques, On Generalized Cullen and Woodall Numbers That are Also Fibonacci Numbers, Journal of Integer Sequences, Vol. 17 (2014), Article 14.9.4.
Hisanori Mishima, Factorizations of many number sequences, Cullen numbers (n = 1 to 100), (n = 101 to 200), (n = 201 to 300), (n = 301 to 323).
Simon Plouffe, Approximations de Séries Génératrices et Quelques Conjectures, Dissertation, Université du Québec à Montréal, 1992.
Simon Plouffe, 1031 Generating Functions, Appendix to Thesis, Montreal, 1992.
Wacław Sierpiński, Elementary Theory of Numbers, Warszawa 1964.
Amelia Carolina Sparavigna, On the generalized sums of Mersenne, Fermat, Cullen and Woodall Numbers, Politecnico di Torino (Italy, 2019).
Amelia Carolina Sparavigna, Composition Operations of Generalized Entropies Applied to the Study of Numbers, International Journal of Sciences, Vol. 8, No. 4 (2019), pp. 87-92.
Amelia Carolina Sparavigna, The groupoids of Mersenne, Fermat, Cullen, Woodall and other Numbers and their representations by means of integer sequences, Politecnico di Torino, Italy (2019), [math.NT].
Amelia Carolina Sparavigna, Some Groupoids and their Representations by Means of Integer Sequences, International Journal of Sciences, Vol. 8, No. 10 (2019).
Eric Weisstein's World of Mathematics, Cullen Number.
Wikipedia, Cullen number.
Index entries for linear recurrences with constant coefficients, signature (5,-8,4).

Cf. A005849, A003261, A050914, A130197, A134081, A001787, A143038, A156708, A181527.
Cf. A000325, A186947.
Diagonal k = n + 1 of A046688.
A000005 counts divisors of n.
A000312 = n^n.
A002109 gives hyperfactorials (sigma: A260146, omega: A303281).
A057156 = (2^n)^(2^n).
A062319 counts divisors of n^n.
A173339 lists positions of squares in A062319.
A188385 gives the highest prime exponent in n^n.
A249784 counts divisors of n^n^n.
Cf. A000169, A000272, A036289, A066959, A176029, A340841, A343656.

a002064 n = n * 2 ^ n + 1
a002064_list = 1 : 3 : (map (+ 1) $ zipWith (-) (tail xs) xs)
   where xs = map (* 4) a002064_list
-- Reinhard Zumkeller, Mar 16 2013

[n*2^n + 1: n in [0..40]]; // Vincenzo Librandi, May 07 2015

A002064:=-(1-2*z+2*z**2)/((z-1)*(-1+2*z)**2); # conjectured by Simon Plouffe in his 1992 dissertation

Table[n*2^n+1,{n,0,2*4!}] (* Vladimir Joseph Stephan Orlovsky, Apr 25 2010 *)
LinearRecurrence[{5,-8,4},{1,3,9},51] (* Harvey P. Dale, Oct 13 2011 *)
CoefficientList[Series[(1 - 2 x + 2 x^2)/((1 - x) (2 x - 1)^2), {x, 0, 50}], x] (* Vincenzo Librandi, May 07 2015 *)

A002064(n)=n*2^n+1  \\ M. F. Hasler, Oct 31 2012

a(n) = 4a(n-1) - 4a(n-2) + 1. - Paul Barry, Jun 12 2003
a(n) = sum of row (n+1) of triangle A130197. Example: a(3) = 25 = (12 + 8 + 4 + 1), row 4 of A130197. - Gary W. Adamson, May 16 2007
Row sums of triangle A134081. - Gary W. Adamson, Oct 07 2007
Equals row sums of triangle A143038. - Gary W. Adamson, Jul 18 2008
Equals row sums of triangle A156708. - Gary W. Adamson, Feb 13 2009
G.f.: -(1-2*x+2*x^2)/((-1+x)*(2*x-1)^2). a(n) = A001787(n+1)+1-A000079(n). - R. J. Mathar, Nov 16 2007
a(n) = 1 + 2^(n + log_2(n)) ~ 1 + A000079(n+A004257(n)). a(n) ~ A000051(n+A004257(n)). - Jonathan Vos Post, Jul 20 2008
a(0)=1, a(1)=3, a(2)=9, a(n) = 5*a(n-1)-8*a(n-2)+4*a(n-3). - Harvey P. Dale, Oct 13 2011
a(n) = A036289(n) + 1 = A003261(n) + 2. - Reinhard Zumkeller, Mar 16 2013
E.g.f.: 2*x*exp(2*x) + exp(x). - Robert Israel, Dec 12 2014
a(n) = 2^n * A000325(n) = 4^n * A186947(-n) for all n in Z. - Michael Somos, Jul 18 2018
a(n) = Sum_{i=0..n-1} a(i) + A000325(n+1). - Ivan N. Ianakiev, Aug 07 2019
a(n) = sigma((2^n)^(2^n)) = A000005(A057156(n)) = A062319(2^n). - Gus Wiseman, May 03 2021
Sum_{n>=0} 1/a(n) = A340841. - Amiram Eldar, Jun 05 2021

Edited by M. F. Hasler, Oct 31 2012

A329193 a(n) = floor(log_2(n^3)) = floor(3 log_2(n)).

Original entry on oeis.org

0, 3, 4, 6, 6, 7, 8, 9, 9, 9, 10, 10, 11, 11, 11, 12, 12, 12, 12, 12, 13, 13, 13, 13, 13, 14, 14, 14, 14, 14, 14, 15, 15, 15, 15, 15, 15, 15, 15, 15, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 17, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18, 18

Offset: 1

M. F. Hasler, Nov 07 2019

nonn

3*A000523(n) <= A000523(n^3) = a(n) <= A004257(n^3) <= A029837(n^3) <= 3*A029837(n) with equality for powers of 2 (A000079) and asymptotic equivalence as n -> oo.

Cf. A000578 (n^3), A000523 (floor log_2), A004257 (round log_2), A029837 (ceiling log_2), A329202 (log_2(n^2)).

apply( A329193(n)=exponent(n^3), [1..99]) \\ exponent(.) = logint(.,2) = log(.)\log(2)

A092757 Partial sums of round(log_2(n)).

Original entry on oeis.org

0, 1, 3, 5, 7, 10, 13, 16, 19, 22, 25, 29, 33, 37, 41, 45, 49, 53, 57, 61, 65, 69, 74, 79, 84, 89, 94, 99, 104, 109, 114, 119, 124, 129, 134, 139, 144, 149, 154, 159, 164, 169, 174, 179, 184, 190, 196, 202, 208, 214, 220, 226, 232, 238, 244, 250, 256, 262, 268, 274

Offset: 1

Jorge Coveiro, Apr 13 2004

Cf. A092919. - R. J. Mathar, Sep 08 2008

A004257 := proc(n) option remember ; round(log[2](n)) ; end: A092757 := proc(n) local i ; add( A004257(i),i=1..n) ; end: for n from 1 to 100 do printf("%d,",A092757(n)) ; od: # R. J. Mathar, Sep 08 2008

Accumulate[Round[Log[2,Range[60]]]] (* Harvey P. Dale, Apr 15 2018 *)

a(n)= sum_{i=1..n} A004257(i). - R. J. Mathar, Sep 08 2008

Corrected and extended by Pab Ter (pabrlos(AT)yahoo.com), May 24 2004

Changed from a(3) on by R. J. Mathar, Sep 08 2008

A225668 a(n) = floor(4*log_2(n)).

Original entry on oeis.org

0, 4, 6, 8, 9, 10, 11, 12, 12, 13, 13, 14, 14, 15, 15, 16, 16, 16, 16, 17, 17, 17, 18, 18, 18, 18, 19, 19, 19, 19, 19, 20, 20, 20, 20, 20, 20, 20, 21, 21, 21, 21, 21, 21, 21, 22, 22, 22, 22, 22, 22, 22, 22, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 24

Offset: 1

Jonathan Vos Post, May 11 2013

Arises in analysis of "when to clean your room".

			a(3) = floor(4*log_2(3)) = floor(6.33985000) = 6.
a(8) = floor(4*log_2(8)) = floor(4*3) = 12.

Kimball Martin and Krishnan Shankar, How often should you clean your room?, arXiv:1305.1984 [math.CO], 2013-2014.

Cf. A000583 (n^4), A000523 (floor log_2), A004257 (round log_2), A029837 (ceiling log_2).

Cf. A329202 (log_2(n^2)), A329193 (log_2(n^3)).

A225668 := proc(n)
    4*log[2](n) ;
    floor(%) ;
end proc: # R. J. Mathar, May 12 2013

Table[Floor[4*Log[2, n]], {n, 1, 64}] (* Jean-François Alcover, Nov 30 2017 *)

a(n) = 4*log(n)\log(2); \\ Michel Marcus, Nov 30 2017

apply( A225668(n)=exponent(n^4), [1..99]) \\ M. F. Hasler, Nov 07 2019

a(n) = floor(4*log(n)/log(2)).

a(n) = floor(log_2(n^4)) = A000523(A000583(n)), i.e., this A225668 = A000523 o A000583. - M. F. Hasler, Nov 07 2019

Better definition from M. F. Hasler, Nov 07 2019

A258782 Nearest integer to log_2(n!).

Original entry on oeis.org

0, 0, 1, 3, 5, 7, 9, 12, 15, 18, 22, 25, 29, 33, 36, 40, 44, 48, 53, 57, 61, 65, 70, 74, 79, 84, 88, 93, 98, 103, 108, 113, 118, 123, 128, 133, 138, 143, 149, 154, 159, 165, 170, 175, 181, 186, 192, 197, 203, 209, 214, 220, 226, 231, 237, 243, 249, 254, 260, 266, 272, 278, 284, 290, 296, 302, 308, 314

Offset: 0

Eli Sadoff, Jun 10 2015

			a(6) = round(log_2(6!)) = round(9.49...) = 9.

Cf. A025201, A067850.

for i = 1:20 { disp(round(log2(factorial(i)))) } end

[Round(LogGamma(n+1)/Log(2)): n in [0..70]]; // Bruno Berselli, Jun 23 2015

seq(round(lnGAMMA(n+1)/ln(2)),n=0..100); # Robert Israel, Jun 10 2015

Round[Log[2, Range[0, 100]! ]] (* Giovanni Resta, Jun 10 2015 *)

a(n) = round(log(n!)/log(2)); \\ Michel Marcus, Jun 10 2015

a(n)=round(lngamma(n+1)/log(2)) \\ Charles R Greathouse IV, Jun 10 2015

[round(log_gamma(n+1)/log2) for n in (0..70)] # Bruno Berselli, Jun 23 2015

a(n) = round(log_2(n!)).
a(n) = A004257(A000142(n)). - Michel Marcus, Jun 10 2015
a(n) = round(Sum_{k=1..n} log_2(k)). - Tom Edgar, Jun 10 2015
a(n) is within 1 of n*(log(n)-1)/log(2) + log(n)/(2*log(2)) + log(sqrt(2*Pi))/log(2) for n >= 1. - Robert Israel, Jun 10 2015

cp's OEIS Frontend

A002064 Cullen numbers: a(n) = n*2^n + 1.

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A329193 a(n) = floor(log_2(n^3)) = floor(3 log_2(n)).

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A092757 Partial sums of round(log_2(n)).

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A225668 a(n) = floor(4*log_2(n)).

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A258782 Nearest integer to log_2(n!).

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A329199 a(n) = round(log_3(n)).

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