cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-10 of 18 results. Next

A006094 Products of 2 successive primes.

Original entry on oeis.org

6, 15, 35, 77, 143, 221, 323, 437, 667, 899, 1147, 1517, 1763, 2021, 2491, 3127, 3599, 4087, 4757, 5183, 5767, 6557, 7387, 8633, 9797, 10403, 11021, 11663, 12317, 14351, 16637, 17947, 19043, 20711, 22499, 23707, 25591, 27221, 28891, 30967, 32399, 34571, 36863
Offset: 1

Views

Author

Keywords

Comments

The Huntley reference would suggest prefixing the sequence with an initial 4 - Enoch Haga. [But that would conflict with the definition! - N. J. A. Sloane, Oct 13 2009]
Sequence appears to coincide with the sequence of numbers n such that the largest prime < sqrt(n) and the smallest prime > sqrt(n) divide n. - Benoit Cloitre, Apr 04 2002
This is true: p(n) < [ sqrt(a(n)) = sqrt(p(n)*p(n+1)) ] < p(n+1) by definition. - Jon Perry, Oct 02 2013
a(n+1) = smallest number such that gcd(a(n), a(n+1)) = prime(n+1). - Alexandre Wajnberg and Ray Chandler, Oct 14 2005
Also the area of rectangles whose side lengths are consecutive primes. E.g., the consecutive primes 7,11 produce a 7 X 11 unit rectangle which has area 77 square units. - Cino Hilliard, Jul 28 2006
a(n) = A001358(A172348(n)); A046301(n) = lcm(a(n), a(n+1)); A065091(n) = gcd(a(n), a(n+1)); A066116(n+2) = a(n+1)*a(n); A109805(n) = a(n+1) - a(n). - Reinhard Zumkeller, Mar 13 2011
See A209329 for the sum of the reciprocals. - M. F. Hasler, Jan 22 2013
A078898(a(n)) = 3. - Reinhard Zumkeller, Apr 06 2015

References

  • H. E. Huntley, The Divine Proportion, A Study in Mathematical Beauty. New York: Dover, 1970. See Chapter 13, Spira Mirabilis, especially Fig. 13-5, page 173.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Subset of the squarefree semiprimes, A006881.
Subsequence of A256617 and A097889.

Programs

  • Haskell
    a006094 n = a006094_list !! (n-1)
    a006094_list = zipWith (*) a000040_list a065091_list
    -- Reinhard Zumkeller, Mar 13 2011
    
  • Haskell
    a006094_list = pr a000040_list
      where pr (n:m:tail) = n*m : pr (m:tail)
            pr _ = []
    -- Jean-François Antoniotti, Jan 08 2020
    
  • Magma
    [NthPrime(n)*NthPrime(n+1): n in [1..41]]; // Bruno Berselli, Feb 24 2011
    
  • Maple
    a:= n-> (p-> p(n)*p(n+1))(ithprime):
    seq(a(n), n=1..43);  # Alois P. Heinz, Jan 02 2021
  • Mathematica
    Table[ Prime[n] Prime[n + 1], {n, 40}] (* Robert G. Wilson v, Jan 22 2004 *)
    Times@@@Partition[Prime[Range[60]], 2, 1] (* Harvey P. Dale, Oct 15 2011 *)
  • MuPAD
    ithprime(i)*ithprime(i+1) $ i = 1..41 // Zerinvary Lajos, Feb 26 2007
    
  • PARI
    g(n) = for(x=1,n,print1(prime(x)*prime(x+1)",")) \\ Cino Hilliard, Jul 28 2006
    
  • PARI
    is(n)=my(p=precprime(sqrtint(n))); p>1 && n%p==0 && isprime(n/p) && nextprime(p+1)==n/p \\ Charles R Greathouse IV, Jun 04 2014
    
  • Python
    from sympy import prime, primerange
    def aupton(nn):
        alst, prevp = [], 2
        for p in primerange(3, prime(nn+1)+1): alst.append(prevp*p); prevp = p
        return alst
    print(aupton(43)) # Michael S. Branicky, Jun 15 2021
    
  • Python
    from sympy import prime, nextprime
    def A006094(n): return (p:=prime(n))*nextprime(p) # Chai Wah Wu, Oct 18 2024

Formula

A209329 = Sum_{n>=2} 1/a(n). - M. F. Hasler, Jan 22 2013
a(n) = A000040(n) * A000040(n+1). - Alois P. Heinz, Jan 02 2021

A046301 Product of 3 successive primes.

Original entry on oeis.org

30, 105, 385, 1001, 2431, 4199, 7429, 12673, 20677, 33263, 47027, 65231, 82861, 107113, 146969, 190747, 241133, 290177, 347261, 409457, 478661, 583573, 716539, 871933, 1009091, 1113121, 1201289, 1317919, 1564259, 1879981, 2279269, 2494633, 2837407, 3127361, 3532343
Offset: 1

Views

Author

Patrick De Geest, Jun 15 1998

Keywords

Examples

			From _K. D. Bajpai_, Aug 27 2014: (Start)
a(2) = 105 is in the sequence because 105 = 3* 5 * 7, product of three successive primes.
a(3) = 385 is in the sequence because 385 = 5 * 7 * 11, product of three successive primes.
(End)
		

Crossrefs

Programs

  • Haskell
    a046301 n = a046301_list !! (n-1)
    a046301_list = zipWith3 (((*) .) . (*))
                   a000040_list (tail a000040_list) (drop 2 a000040_list)
    -- Reinhard Zumkeller, May 12 2015
  • Magma
    [NthPrime(n)*NthPrime(n+1)*NthPrime(n+2): n in [1..31]]; /* Or: */ [&*[ NthPrime(n+k): k in [0..2] ]: n in [1..31] ]; // Bruno Berselli, Feb 25 2011
    
  • Maple
    A046301:=n->ithprime(n)*ithprime(n+1)*ithprime(n+2): seq(A028560(n), n=1..100);  # K. D. Bajpai, Aug 27 2014
  • Mathematica
    Table[Prime[n] Prime[n+1] Prime[n+2],{n,50}]   (* K. D. Bajpai, Aug 27 2014 *)
    Times@@@Partition[Prime[Range[40]],3,1] (* Harvey P. Dale, Mar 25 2019 *)
  • PARI
    a(n)=prime(n)*prime(n+1)*prime(n+2); \\ Joerg Arndt, Aug 30 2014
    

Formula

Sum_{n>=1} 1/a(n) = A242187. - Amiram Eldar, Nov 19 2020

Extensions

Offset changed from 0 to 1 by Vincenzo Librandi, Jan 16 2012

A046303 Product of 5 successive primes.

Original entry on oeis.org

2310, 15015, 85085, 323323, 1062347, 2800733, 6678671, 14535931, 31367009, 58642669, 95041567, 162490421, 259106347, 385499687, 600662303, 907383479, 1249792339, 1673450759, 2276990377, 3024658859, 4132280413, 5717264681
Offset: 1

Views

Author

Patrick De Geest, Jun 15 1998

Keywords

Crossrefs

Programs

  • Magma
    [&*[ NthPrime(n+k): k in [0..4] ]: n in [1..22]];  // Bruno Berselli, Feb 25 2011
    
  • Mathematica
    lst={};Do[p0=Prime[n];p1=Prime[n+1];p2=Prime[n+2];p3=Prime[n+3];p4=Prime[n+4];a=p0*p1*p2*p3*p4;AppendTo[lst,a],{n,5!}];lst (* Vladimir Joseph Stephan Orlovsky, Mar 10 2009 *)
    Times@@@Partition[Prime[Range[200]],5,1] (* Harvey P. Dale, Oct 21 2011 *)
  • PARI
    first(n)=my(P=primes(n+4)); vector(n,i,prod(j=i,i+4,P[j])) \\ Charles R Greathouse IV, Jun 27 2019

Formula

a(n) = Product_{j=n..n+4} prime(j). - Jon E. Schoenfield, Jan 07 2015
a(n) ~ (n log n)^5. - Charles R Greathouse IV, Jun 27 2019

A046324 Product of 6 successive primes.

Original entry on oeis.org

30030, 255255, 1616615, 7436429, 30808063, 86822723, 247110827, 595973171, 1348781387, 2756205443, 5037203051, 9586934839, 15805487167, 25828479029, 42647023513, 66238993967, 98733594781, 138896412997, 202652143553
Offset: 1

Views

Author

Patrick De Geest, Jun 15 1998

Keywords

Crossrefs

Programs

  • Magma
    [&*[ NthPrime(n+k): k in [0..5] ]: n in [1..19] ];  // Bruno Berselli, Feb 25 2011
  • Mathematica
    Times@@@Partition[Prime[Range[200]],6,1] (* Harvey P. Dale, Oct 21 2011 *)

Extensions

Offset changed from 0 to 1 by Vincenzo Librandi, Jan 16 2012

A046326 Product of 8 successive primes.

Original entry on oeis.org

9699690, 111546435, 1078282205, 6685349671, 35336848261, 131710070791, 435656388001, 1204461778591, 3359814435017, 8618654420261, 18128893780549, 39181802686993, 75186702453419, 133869006807307, 245945384599471
Offset: 1

Views

Author

Patrick De Geest, Jun 15 1998

Keywords

Crossrefs

Cf. A002110.
Cf. product of n successive primes: A006094, A046301, A046302, A046303, A046324, A046325, A046327.

Programs

  • Magma
    [&*[ NthPrime(n+k): k in [0..7] ]: n in [1..15]];  // Bruno Berselli, Feb 25 2011
  • Mathematica
    Times@@@Partition[Prime[Range[50]],8,1] (* Harvey P. Dale, Oct 21 2011 *)

Extensions

Offset changed from 0 to 1 by Vincenzo Librandi, Jan 16 2012

A046327 Numbers that are the product of 9 successive primes.

Original entry on oeis.org

223092870, 3234846615, 33426748355, 247357937827, 1448810778701, 5663533044013, 20475850236047, 63836474265323, 198229051666003, 525737919635921, 1214635883296783, 2781907990776503, 5488629279099587
Offset: 1

Views

Author

Patrick De Geest, Jun 15 1998

Keywords

Crossrefs

Cf. A002110.
Cf. product of n successive primes: A006094, A046301, A046302, A046303, A046324, A046326.

Programs

Formula

a(n) = Product_{j=n..n+8} prime(j). - Jon E. Schoenfield, Jan 07 2015

Extensions

More terms from Vladimir Joseph Stephan Orlovsky, Aug 26 2008
Offset changed from 0 to 1 by Vincenzo Librandi, Jan 16 2012

A046325 Product of 7 successive primes.

Original entry on oeis.org

510510, 4849845, 37182145, 215656441, 955049953, 3212440751, 10131543907, 25626846353, 63392725189, 146078888479, 297194980009, 584803025179, 1058967640189, 1833822011059, 3113232716449, 5232880523393, 8194888366823
Offset: 1

Views

Author

Patrick De Geest, Jun 15 1998

Keywords

Crossrefs

Cf. A002110.
Cf. product of n successive primes: A006094, A046301, A046302, A046303, A046324, A046326, A046327.

Programs

  • Magma
    [&*[ NthPrime(n+k): k in [0..6] ]: n in [1..17]];  // Bruno Berselli, Feb 25 2011
  • Mathematica
    Times@@@Partition[Prime[Range[50]],7,1] (* Harvey P. Dale, Oct 21 2011 *)

Extensions

Offset changed from 0 to 1 by Vincenzo Librandi, Jan 16 2012

A097889 Numbers that are products of (at least two) consecutive primes.

Original entry on oeis.org

6, 15, 30, 35, 77, 105, 143, 210, 221, 323, 385, 437, 667, 899, 1001, 1147, 1155, 1517, 1763, 2021, 2310, 2431, 2491, 3127, 3599, 4087, 4199, 4757, 5005, 5183, 5767, 6557, 7387, 7429, 8633, 9797, 10403, 11021, 11663, 12317, 12673, 14351, 15015, 16637, 17017
Offset: 1

Views

Author

Bart la Bastide (bart(AT)xs4all.nl), Sep 21 2004

Keywords

Comments

Subsequence of A073485; A073490(a(n)) = 0. - Reinhard Zumkeller, Nov 20 2004
A proper subset of A073485. - Robert G. Wilson v, Jun 11 2010
A192280(a(n)) * (1 - A010051(a(n))) = 1. - Reinhard Zumkeller, Aug 26 2011 [corrected by Jason Yuen, Aug 29 2024]
The Heinz numbers of the partitions into at least 2 consecutive parts. The Heinz number of an integer partition p = [p_1, p_2, ..., p_r] is defined as Product(p_j-th prime, j=1...r) (concept used by Alois P. Heinz in A215366 as an "encoding" of a partition). Examples: (i) 105 (=3*5*7) is in the sequence because it is the Heinz number of the partition [2,3,4]; (ii) 108 (= 2*2*3*3*3) is not in the sequence because it is the Heinz number of the partition [1,1,2,2,2]. - Emeric Deutsch, Oct 02 2015

Examples

			1001 = 7 * 11 * 13.
		

Crossrefs

Cf. A050936.
Intersection of A073485 and A002808.

Programs

  • Haskell
    import Data.Set (singleton, deleteFindMin, insert)
    a097889 n = a097889_list !! (n-1)
    a097889_list = f $ singleton (6, 2, 3) where
       f s = y : f (insert (w, p, q') $ insert (w `div` p, a151800 p, q') s')
             where w = y * q'; q' = a151800 q
                   ((y, p, q), s') = deleteFindMin s
    -- Reinhard Zumkeller, May 12 2015, Aug 26 2011
    
  • Maple
    isA097889 := proc(n)
        local plist,p,i ;
        plist := sort(convert(numtheory[factorset](n),list)) ;
        if nops(plist) < 2 then
            return false;
        end if;
        for i from 1 to nops(plist) do
            p := op(i,plist) ;
            if modp(n,p^2) = 0 then
                return false;
            end if;
            if i > 1 then
                if nextprime(op(i-1,plist)) <> p then
                    return false;
                end if;
            end if;
        end do:
        true;
    end proc:
    for n from 1 to 1000 do
        if isA097889(n) then
            printf("%d,",n);
        end if;
    end do: # R. J. Mathar, Jan 12 2016
  • Mathematica
    a = {}; Do[ AppendTo[a, Apply[ Times, (Prime /@ Partition[ Range[30], n, i]), 1]], {n, 2, 6}, {i, n - 1}]; Take[ Union[ Flatten[ a]], 45] (* Robert G. Wilson v, Sep 24 2004 *)
  • PARI
    list(lim)=my(v=List(), p, t); for(e=2, log(lim+.5)\log(2), p=1; t=prod(i=1, e-1, prime(i)); forprime(q=prime(e), lim, t*=q/p; if(t>lim, next(2)); listput(v, t); p=nextprime(p+1))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Oct 24 2012
    
  • Python
    import heapq
    from sympy import sieve
    sieve.extend(10**6)
    primes = list(sieve._list)
    def prime(n): return primes[n-1]
    def aupton(terms, verbose=False):
        p = prime(1)*prime(2); h = [(p, 1, 2)]; nextcount = 3; alst = []
        while len(alst) < terms:
            (v, s, l) = heapq.heappop(h)
            alst.append(v)
            if verbose: print(f"{v}, [= Prod_{{i = {s}..{l}}} prime(i)]")
            if v >= p:
                p *= prime(nextcount)
                heapq.heappush(h, (p, 1, nextcount))
                nextcount += 1
            v //= prime(s); s += 1; l += 1; v *= prime(l)
            heapq.heappush(h, (v, s, l))
        return alst
    print(aupton(45)) # Michael S. Branicky, Jun 15 2021

Formula

a(n) ~ n^2 log^2 n. - Charles R Greathouse IV, Oct 24 2012

Extensions

More terms from Robert G. Wilson v, Sep 24 2004
Data corrected for n > 41 by Reinhard Zumkeller, Aug 26 2011

A255483 Infinite square array read by antidiagonals downwards: T(0,m) = prime(m), m >= 1; for n >= 1, T(n,m) = T(n-1,m)*T(n-1,m+1)/gcd(T(n-1,m), T(n-1,m+1))^2, m >= 1.

Original entry on oeis.org

2, 3, 6, 5, 15, 10, 7, 35, 21, 210, 11, 77, 55, 1155, 22, 13, 143, 91, 5005, 39, 858, 17, 221, 187, 17017, 85, 3315, 1870, 19, 323, 247, 46189, 133, 11305, 5187, 9699690, 23, 437, 391, 96577, 253, 33649, 21505, 111546435, 46
Offset: 0

Views

Author

N. J. A. Sloane, Feb 28 2015

Keywords

Comments

The first column of the array is given by A123098; subsequent columns are obtained by applying the function A003961, i.e., replacing each prime factor by the next larger prime. - M. F. Hasler, Sep 17 2016
Interpretation with respect to A329329 from Peter Munn, Feb 08 2020: (Start)
With respect to the ring defined by A329329 and A059897, the first row gives powers of 3, the first column gives powers of 6, both in order of increasing exponent, and the body of the table gives their products. A329049 is the equivalent table in which the first column gives powers of 4.
A099884 is the equivalent table for the ring defined by A048720 and A003987. That ring is an image of the polynomial ring GF(2)[x] using a standard representation of the polynomials as integers. A329329 describes a comparable mapping to integers from the related polynomial ring GF(2)[x,y].
Using these mappings, the tables here and in A099884 are matching images: the first row represents powers of x, the first column represents powers of (x+1) and the body of the table gives their products.
Hugo van der Sanden's formula (see formula section) indicates that A019565 provides a mapping from A099884. In the wider terms described above, A019565 is an injective homomorphism between images of the 2 polynomial rings, and maps the image of each GF(2)[x] polynomial to the image of the equivalent GF(2)[x,y] polynomial.
(End)

Examples

			The top left corner of the array, row index 0..5, column index 1..10:
    2,    3,     5,     7,    11,     13,     17,     19,      23,      29
    6,   15,    35,    77,   143,    221,    323,    437,     667,     899
   10,   21,    55,    91,   187,    247,    391,    551,     713,    1073
  210, 1155,  5005, 17017, 46189,  96577, 215441, 392863,  765049, 1363783
   22,   39,    85,   133,   253,    377,    527,    703,     943,    1247
  858, 3315, 11305, 33649, 95381, 198679, 370481, 662929, 1175921, 1816879
		

Crossrefs

First two columns = A123098, A276804.
A kind of generalization of A036262.
Transpose: A276578, terms sorted into ascending order: A276579.
A003987, A048720, A059897, A329049 relate to the A329329 polynomial ring interpretation.

Programs

  • Maple
    T:= proc(n, m) option remember; `if`(n=0, ithprime(m),
          T(n-1, m)*T(n-1, m+1)/igcd(T(n-1, m), T(n-1, m+1))^2)
        end:
    seq(seq(T(n, 1+d-n), n=0..d), d=0..10);  # Alois P. Heinz, Feb 28 2015
  • Mathematica
    T[n_, m_] := T[n, m] = If[n == 0, Prime[m], T[n-1, m]*T[n-1, m+1]/GCD[T[n-1, m], T[n-1, m+1]]^2]; Table[Table[T[n, 1+d-n], {n, 0, d}], {d, 0, 10}] // Flatten (* Jean-François Alcover, Mar 09 2015, after Alois P. Heinz *)
  • PARI
    T=matrix(N=15,N);for(j=1,N,T[1,j]=prime(j));(f(x,y)=x*y/gcd(x,y)^2);for(k=1,N-1,for(j=1,N-k,T[k+1,j]=f(T[k,j],T[k,j+1])));A255483=concat(vector(N,i,vector(i,j,T[j,1+i-j]))) \\ M. F. Hasler, Sep 17 2016
    
  • PARI
    A255483(n,k)=prod(j=0,n,if(bitand(n-j,j),1,prime(j+k))) \\ M. F. Hasler, Sep 18 2016
    
  • Scheme
    (define (A255483 n) (A255483bi (A002262 n) (+ 1 (A025581 n))))
    ;; Then use either an almost standalone version (requiring only A000040):
    (define (A255483bi row col) (if (zero? row) (A000040 col) (let ((a (A255483bi (- row 1) col)) (b (A255483bi (- row 1) (+ col 1)))) (/ (lcm a b) (gcd a b)))))
    ;; Or one based on M. F. Hasler's new recurrence:
    (define (A255483bi row col) (if (= 1 col) (A123098 row) (A003961 (A255483bi row (- col 1)))))
    ;; Antti Karttunen, Sep 18 2016

Formula

T(n,1) = A123098(n), T(n,m+1) = A003961(T(n,m)), for all n >= 0, m >= 1. - M. F. Hasler, Sep 17 2016
T(n,m) = Prod_{k=0..n} prime(k+m)^(!(n-k & k)) where !x is 1 if x=0 and 0 else, and & is binary AND. - M. F. Hasler, Sep 18 2016
From Antti Karttunen, Sep 18 2016: (Start)
For n >= 1, m >= 1, T(n,m) = lcm(T(n-1,m),T(n-1,m+1)) / gcd(T(n-1,m),T(n-1,m+1)).
T(n,k) = A007913(A066117(n+1,k)).
T(n,k) = A019565(A099884(n,k-1)) [After Hugo van der Sanden's observations on SeqFan-list].
(End)
From Peter Munn, Jan 08 2020: (Start)
T(0,1) = 2, and for n >= 0, k >= 1, T(n+1,k) = A329329(T(n,k), 6), T(n,k+1) = A329329(T(n,k), 3).
T(n,k) = A329329(T(n,1), T(0,k)).
(End)

A127346 Primes in A127345.

Original entry on oeis.org

31, 71, 167, 311, 1151, 3119, 4871, 5711, 6791, 14831, 24071, 33911, 60167, 79031, 101159, 106367, 115631, 158231, 235751, 259751, 366791, 402551, 455471, 565919, 635711, 644951, 1124831, 1347971, 1510799, 1547927, 1743419, 1851671, 2048471
Offset: 1

Views

Author

Artur Jasinski, Jan 11 2007

Keywords

Comments

Primes of the form prime(k)*prime(k+1) + prime(k)*prime(k+2) + prime(k+1)*prime(k+2).
A prime number n is in the sequence if for some k it is the coefficient of x^1 of the polynomial Product_{j=0..2} (x-prime(k+j)); the roots of this polynomial are prime(k), ..., prime(k+2).

Crossrefs

Programs

  • Mathematica
    b = {}; a = {}; Do[If[PrimeQ[Prime[x] Prime[x + 1] + Prime[x] Prime[x + 2] + Prime[x + 1] Prime[x + 2]], AppendTo[a, Prime[x] Prime[x + 1] + Prime[x] Prime[x + 2] + Prime[x + 1] Prime[x + 2]], AppendTo[b, Prime[x] Prime[x + 1] + Prime[x] Prime[x + 2] + Prime[x + 1] Prime[x + 2]]], {x, 1, 100}]; Print[a] (* Artur Jasinski, Jan 11 2007 *)
    s[li_] := li[[1]]*(li[[2]]+li[[3]])+li[[2]]*li[[3]]; Select[(s[#]&/@Partition[Prime[Range[100]], 3, 1]), PrimeQ] (* Zak Seidov, Jan 13 2012 *)
  • PARI
    {m=143;k=2;for(n=1,m,a=sum(i=n,n+k-1,sum(j=i+1,n+k,prime(i)*prime(j)));if(isprime(a),print1(a,",")))} \\ Klaus Brockhaus, Jan 21 2007
    
  • PARI
    {m=143;k=2;for(n=1,m,a=polcoeff(prod(j=0,k,(x-prime(n+j))),1);if(isprime(a),print1(a,",")))} \\ Klaus Brockhaus, Jan 21 2007
    
  • PARI
    p=2; q=3; forprime(r=5, 1e3, if(isprime(t=p*q+p*r+q*r), print1(t", ")); p=q; q=r) \\ Charles R Greathouse IV, Jan 13 2012

Formula

a(n) = A127345(A204231(n)). - Zak Seidov, Jan 13 2012

Extensions

Edited and extended by Klaus Brockhaus, Jan 21 2007
Showing 1-10 of 18 results. Next