A037461 -id:A037461 - cp's OEIS frontend

A030979 Numbers k such that binomial(2k,k) is not divisible by 3, 5 or 7.

0, 1, 10, 756, 757, 3160, 3186, 3187, 3250, 7560, 7561, 7651, 20007, 59548377, 59548401, 45773612811, 45775397187, 237617431723407, 24991943420078301, 24991943420078302, 24991943420078307, 24991943715007536, 24991943715007537

Offset: 1

Shawn Godin (sgodin(AT)onlink.net)

nonn

By Lucas's theorem, binomial(2k,k) is not divisible by a prime p iff all base-p digits of k are smaller than p/2.
Ronald L. Graham offered $1000 to the first person who could settle the question of whether this sequence is finite or infinite. He remarked that heuristic arguments show that it should be infinite, but finite if it is required that binomial(2k,k) is prime to 3, 5, 7 and 11, with k = 3160 probably the last k which has this property.
The Erdős et al. paper shows that for any two odd primes p and q there are an infinite number of k for which gcd(p*q,binomial(2k,k))=1; i.e., p and q do not divide binomial(2k,k). The paper does not deal with the case of three primes. - T. D. Noe, Apr 18 2007
Pomerance gives a heuristic suggesting that there are on the order of x^0.02595... terms up to x. - Charles R Greathouse IV, Oct 09 2015

R. K. Guy, Unsolved Problems in Number Theory, Springer, 1st edition, 1981. See section B33.

Christopher E. Thompson, Table of n, a(n) for n = 1..1374 (complete up to 10^70, extends first 62 terms computed by Max Alekseyev).
Christian Ballot, Divisibility of the middle Lucasnomial coefficient, Fib. Q., 55 (2017), 297-308.
Ernie Croot, Hamed Mousavi and Maxie Schmidt, On a conjecture of Graham on the p-divisibility of central binomial coefficients, arXiv:2201.11274 [math.NT], 2022.
P. Erdős, R. L. Graham, I. Z. Russa and E. G. Straus, On the prime factors of C(2n,n), Math. Comp. 29 (1975), 83-92, doi:10.2307/2005464.
Gennady Eremin, Factoring Middle Binomial Coefficients, arXiv:2003.01494 [math.CO], 2020.
R. D. Mauldin and S. M. Ulam, Mathematical problems and games, Adv. Appl. Math. 8 (3) (1987) 281-344.
C. Pomerance, Divisors of the middle binomial coefficient, Amer. Math. Monthly, 112 (2015), 636-644.
Wikipedia, Lucas' theorem
Han Yu, Fractal projections with an application in number theory, arXiv:2004.05924 [math.NT], 2020.

Cf. A129488, A129489, A129508, A151750.

lim=10000; Intersection[Table[FromDigits[IntegerDigits[k,2],3], {k,0,lim}], Table[FromDigits[IntegerDigits[k,3],5], {k,0,lim}], Table[FromDigits[IntegerDigits[k,4],7], {k,0,lim}]] (* T. D. Noe, Apr 18 2007 *)

fval(n,p)=my(s);while(n\=p,s+=n);s
is(n)=fval(2*n,3)==2*fval(n,3) && fval(2*n,5)==2*fval(n,5) && fval(2*n,7)==2*fval(n,7) \\ Charles R Greathouse IV, Oct 09 2015

Intersection of A005836, A037453 and A037461. - T. D. Noe, Apr 18 2007

More terms from Naohiro Nomoto, May 06 2002
Additional comments from R. L. Graham, Apr 25 2007
Additional comments and terms up 3^41 in b-file from Max Alekseyev, Nov 23 2008
Additional terms up to 10^70 in b-file from Christopher E. Thompson, Nov 06 2015

A050608 Numbers k such that base 7 expansion matches (0|1|2|3)((0|1|2)(4|5|6))?(0|1|2|3).

Original entry on oeis.org

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 28, 29, 30, 31, 35, 36, 37, 38, 42, 43, 44, 45, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 77, 78, 79, 80, 84, 85, 86, 87, 91, 92, 93, 94, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113

Offset: 1

Antti Karttunen, 1999

49 does not divide C(2s-1,s) = A001700(s) (nor C(2s,s) = A000984(s), central column of Pascal's triangle) if and only if s is one of the terms in this sequence.

Index entries for 7-automatic sequences.

Cf. A037461, A046097, A050607, A051382.

# For conv_x_base_n function, see A050607.
for($i=0; $i <= 1000; $i++) { if(("0" . conv_x_base_n($i,7)) =~ /^(0|1|2|3)*((0|1|2)(4|5|6))?(0|1|2|3)*$/) { print $i, ","; } }

a(1)=0 inserted by Georg Fischer, Jun 26 2021

A295562 List of numbers whose middle Fibonomial coefficient (2n,n)_F is prime to 105.

Original entry on oeis.org

1, 1312, 3256, 3257, 3936, 3937, 4000, 4001, 4032, 38880, 38881, 39000, 39001, 19928280, 19928281, 21975136, 21975137, 21975305, 21975312, 22054032

Offset: 1

N. J. A. Sloane, Nov 28 2017

From Charlie Neder, Mar 04 2019: (Start)
For the middle Fibonomial coefficient (2n,n)_F to be coprime to a prime p, we must have that the integral part of n/A001177(p) has its base-p digits all < p/2 and its fractional part is < 1/2.
Next term > 10^8. (End)

Christian Ballot, Divisibility of the middle Lucasnomial coefficient, Fib. Q., 55 (2017), 297-308.

Cf. A003267, A030979.

Cf. A037461, A037543, A005836.

Numbers k congruent to 0 or 1 modulo 8 such that floor(k/4) is in A005836, k is in A037543, and floor(k/8) is in A037461. - Charlie Neder, Mar 04 2019

a(10)-a(20) from Charlie Neder, Mar 04 2019

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A030979 Numbers k such that binomial(2k,k) is not divisible by 3, 5 or 7.

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A050608 Numbers k such that base 7 expansion matches (0|1|2|3)((0|1|2)(4|5|6))?(0|1|2|3).

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A295562 List of numbers whose middle Fibonomial coefficient (2n,n)_F is prime to 105.

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cp's OEIS Frontend

A030979 Numbers k such that binomial(2k,k) is not divisible by 3, 5 or 7.

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A050608 Numbers k such that base 7 expansion matches (0|1|2|3)*((0|1|2)(4|5|6))?(0|1|2|3)*.

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A295562 List of numbers whose middle Fibonomial coefficient (2n,n)_F is prime to 105.

Views

Author

Keywords

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Links

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Formula

Extensions

A050608 Numbers k such that base 7 expansion matches (0|1|2|3)((0|1|2)(4|5|6))?(0|1|2|3).