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.

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A072583 Numbers k with the property that there is no match when comparing the numbers of 0's and 1's in the binary representations of k and the k-th prime.

Original entry on oeis.org

2, 4, 9, 10, 11, 12, 14, 15, 17, 18, 27, 29, 33, 35, 36, 38, 39, 40, 43, 46, 48, 51, 52, 53, 54, 55, 56, 63, 66, 72, 73, 75, 76, 83, 85, 86, 90, 91, 92, 95, 96, 97, 100, 102, 104, 109, 111, 112, 113, 115, 117, 119, 120, 122, 123, 124, 126, 127, 129, 130, 131, 132, 133
Offset: 1

Views

Author

Reinhard Zumkeller, Jun 23 2002

Keywords

Comments

In other words, A000120(k) <> A000120(A000040(k)) and A000120(k) <> A023416(A000040(k)) and A023416(k) <> A000120(A000040(k)) and A023416(k) <> A023416(A000040(k)).
A000120(k) <> A014499(k) and A000120(k) <> A035103(k) and A023416(k) <> A014499(k) and A023416(k) <> A035103(k).

Examples

			k = 40 = '101000', A000040(40) = 173 = '10101101'.
		

Crossrefs

Programs

  • Mathematica
    With[{m = 150}, Select[Transpose[{Range[m], Prime[Range[m]]}], Intersection @@ DigitCount[#, 2] == {} &]][[;; , 1]] (* Amiram Eldar, Jul 28 2025 *)

Formula

a(n) = A049084(A072584(n)).

A176620 Primes p for which the factorization of p! over distinct terms of A050376 does not contain 2.

Original entry on oeis.org

7, 11, 13, 19, 31, 37, 41, 47, 59, 61, 67, 73, 79, 97, 103, 107, 109, 127, 131, 137, 151, 157, 167, 173, 179, 181, 191, 193, 199, 211, 223, 227, 229, 233, 239, 241, 251, 271, 283, 307, 313, 331, 367, 379, 397, 409, 419, 421, 431, 433, 439, 443, 457, 463, 487
Offset: 1

Views

Author

Vladimir Shevelev, Apr 22 2010

Keywords

Comments

Equivalent definition: primes p for which A007814(p!) is even. Apparently, the sequence is A027697 without the 2 (see A014499). [R. J. Mathar, Oct 26 2010]

Crossrefs

Programs

  • Mathematica
    Select[Range[500], PrimeQ[#] && EvenQ @ IntegerExponent[#!, 2] &]  (* Amiram Eldar, Sep 13 2019 *)

Extensions

Corrected (37 added, 41 added, 43 removed...) and extended by R. J. Mathar, Oct 26 2010

A177835 Primes p for which a smaller prime q exists with A000120(q) >= 2*A000120(p)-1.

Original entry on oeis.org

17, 37, 41, 67, 73, 97, 131, 137, 139, 149, 163, 193, 197, 257, 263, 269, 277, 281, 293, 337, 353, 389, 401, 449, 521, 523, 547, 577, 593, 641, 643, 673, 769, 773, 1031, 1033, 1039, 1049, 1051, 1061, 1063, 1069, 1091, 1093, 1097, 1109, 1123, 1129, 1153, 1163, 1171
Offset: 1

Views

Author

Vladimir Shevelev, May 14 2010

Keywords

Comments

See A177836 for a comparison with A095075.

Crossrefs

Programs

  • Maple
    read("transforms") ;A000120 := proc(n) wt(n) ; end proc:
    isA177835 := proc(p) if isprime(p) then q := 2 ; while q < p do if A000120(q) >= 2*A000120(p)-1 then return true; end if; q := nextprime(q) ; end do: return false; else false; end if; end proc:
    for i from 1 to 2000 do if isA177835(ithprime(i)) then printf("%d,",ithprime(i)) ; end if; end do: # R. J. Mathar, May 31 2010
  • Mathematica
    With[{b = DigitCount[Prime[Range[200]], 2, 1]}, Rest@ Prime[Position[2*b - 1 - FoldList[Max, b], ?(# <= 0 &)] // Flatten]] (* _Amiram Eldar, Jul 25 2023 *)

Extensions

keyword:base and more terms added by R. J. Mathar, May 31 2010

A177836 Terms of A095075 which are not in A177835.

Original entry on oeis.org

2, 541, 557, 563, 569, 587, 601, 613, 617, 647, 653, 659, 661, 677, 709, 787, 809, 929, 2141, 2203, 2221, 2251, 2281, 2333, 2347, 2357, 2381, 2389, 2393, 2417, 2467, 2473, 2617, 2659, 2699, 2707, 2713, 2729, 2837, 2851, 2857, 2897, 2953, 3221, 3347, 3461
Offset: 1

Views

Author

Vladimir Shevelev, May 14 2010

Keywords

Comments

Note that the consecutive terms A095075(2)=17 up to A095075(27)=523 are all in A177835.

Crossrefs

Programs

Formula

Extensions

Keyword:base and more terms from R. J. Mathar, May 31 2010

A239694 Base 8 sum of digits of prime(n).

Original entry on oeis.org

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

Views

Author

Tom Edgar, Mar 24 2014

Keywords

Comments

a(n) is the rank of prime(n) in the base-8 dominance order on the natural numbers.

Examples

			The sixth prime is 13, 13 in base 8 is (1,5) so a(6)=1+5=6.
		

Crossrefs

Programs

  • Magma
    [&+Intseq(NthPrime(n),8): n in [1..100]]; // Vincenzo Librandi, Mar 25 2014
    
  • Mathematica
    Table[Plus @@ IntegerDigits[Prime[n], 8], {n, 1, 100}] (* Vincenzo Librandi, Mar 25 2014 *)
  • PARI
    a(n) = sumdigits(prime(n), 8); \\ Michel Marcus, Mar 04 2023
  • Sage
    [sum(i.digits(base=8)) for i in primes_first_n(200)]
    

Formula

a(n) = A053829(A000040(n)).

A373124 Sum of indices of primes between powers of 2.

Original entry on oeis.org

1, 2, 7, 11, 45, 105, 325, 989, 3268, 10125, 33017, 111435, 369576, 1277044, 4362878, 15233325, 53647473, 189461874, 676856245, 2422723580, 8743378141, 31684991912, 115347765988, 421763257890, 1548503690949, 5702720842940, 21074884894536, 78123777847065
Offset: 0

Views

Author

Gus Wiseman, May 31 2024

Keywords

Comments

Sum of k such that 2^n+1 <= prime(k) <= 2^(n+1).

Examples

			Row-sums of the sequence of all positive integers as a triangle with row-lengths A036378:
   1
   2
   3  4
   5  6
   7  8  9 10 11
  12 13 14 15 16 17 18
  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 50 51 52 53 54
		

Crossrefs

For indices of primes between powers of 2:
- sum A373124 (this sequence)
- length A036378
- min A372684 (except initial terms), delta A092131
- max A007053
For primes between powers of 2:
- sum A293697
- length A036378
- min A104080 or A014210
- max A014234, delta A013603
For squarefree numbers between powers of 2:
- sum A373123
- length A077643, run-lengths of A372475
- min A372683, delta A373125, indices A372540
- max A372889, delta A373126, indices A143658

Programs

  • Mathematica
    Table[Total[PrimePi/@Select[Range[2^(n-1)+1,2^n],PrimeQ]],{n,10}]
  • PARI
    ip(n) = primepi(1<A007053
    t(n) = n*(n+1)/2; \\ A000217
    a(n) = t(ip(n+1)) - t(ip(n)); \\ Michel Marcus, May 31 2024

A129000 Start with an integer (in this case, 1). First, add 5 or 8 if the integer is odd or even, respectively. Then divide by 2.

Original entry on oeis.org

1, 3, 4, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7
Offset: 1

Views

Author

Adam F. Schwartz (adam_s(AT)mit.edu), May 01 2007

Keywords

Examples

			a(7) = 6 because (7 + 5)/2 = 6.
		

Crossrefs

Programs

  • Mathematica
    a={1};k=1;For[n=1,n<70,n++,If[EvenQ[k],k=k+8,k=k+5];k=k/2;AppendTo[a, k]]; a (* Stefan Steinerberger, May 26 2007 *)

Formula

a(n) = (a(n-1) + b)/d, if a(n) even = (a(n-1) + c)/d, if a(n) odd (starting with a(1)=1, b=5, c=8, d=2).

Extensions

More terms from Stefan Steinerberger, May 26 2007

A166007 Number of ones in the binary representation of the middle member q of the prime triple (p,q,r) with p

Original entry on oeis.org

3, 3, 3, 2, 3, 3, 4, 4, 4, 5, 5, 5, 3, 4, 5, 5, 4, 6, 5, 6, 6, 7, 5, 4, 7, 7, 6, 7, 6, 7, 4, 4, 9, 5, 6, 6, 6, 7, 7, 8, 6, 5, 5, 5, 9, 8, 6, 7, 8, 9, 4, 5, 6, 8, 7, 6, 6, 9, 4, 7, 7, 8, 7, 7, 6, 7, 7, 7, 7, 7, 9, 8, 3, 6, 6, 7, 7, 7, 7, 6, 7, 8, 6, 6, 5, 8
Offset: 1

Views

Author

Steven Lubars (lubars(AT)gmail.com), Oct 03 2009

Keywords

Examples

			For n = 3, (p, q, r) = (11, 13, 17), q = 13
Decimal 13 = Binary 1101
a(3) = Number of ones in 1101 = 3
		

Crossrefs

Programs

  • Mathematica
    DigitCount[#,2,1]&/@Transpose[Select[Partition[Prime[Range[1000]],3,1], Last[#]-First[#]==6&]][[2]] (* Harvey P. Dale, Dec 03 2014 *)

Extensions

More terms from Harvey P. Dale, Dec 03 2014

A166008 Number of ones in the binary representation of the average of twin prime pairs.

Original entry on oeis.org

1, 2, 2, 2, 4, 3, 4, 2, 4, 4, 3, 4, 4, 2, 4, 4, 4, 4, 4, 4, 5, 4, 4, 6, 3, 5, 4, 5, 3, 4, 5, 6, 6, 6, 6, 8, 2, 4, 4, 3, 2, 6, 8, 4, 5, 4, 5, 6, 6, 5, 4, 5, 4, 5, 7, 8, 5, 7, 6, 8, 8, 8, 3, 3, 2, 4, 6, 7, 6, 4, 4, 6, 8, 3, 5, 3, 5, 6, 7, 7, 7, 7, 4, 4, 6, 7, 6
Offset: 1

Views

Author

Steven Lubars (lubars(AT)gmail.com), Oct 03 2009

Keywords

Examples

			Third twin prime pair = (11,13) with average 12 = 1100_2, with 2 ones, so a(3)=2.
		

Crossrefs

Programs

  • Magma
    [&+Intseq(p+1,2):p in PrimesUpTo(3000)|IsPrime(p+2)]; // Marius A. Burtea, Dec 19 2019
  • Mathematica
    seq={1}; Do[If[And @@ PrimeQ[6n + {-1, 1}], AppendTo[seq, DigitCount[6n, 2, 1]]], {n, 1, 600}]; seq (* Amiram Eldar, Dec 19 2019 *)
    DigitCount[#,2,1]&/@(Mean/@Select[Partition[Prime[Range[1000]],2,1],#[[2]]- #[[1]] == 2&]) (* Harvey P. Dale, Dec 12 2021 *)

Formula

a(n) = A000120(A014574(n)). - Michel Marcus, Dec 19 2019

Extensions

More terms from Amiram Eldar, Dec 19 2019

A177959 n-th prime minus number of 0's in binary representation of n-th prime.

Original entry on oeis.org

1, 3, 4, 7, 10, 12, 14, 17, 22, 28, 31, 34, 38, 41, 46, 51, 58, 60, 63, 68, 69, 77, 80, 86, 93, 98, 101, 105, 107, 110, 127, 126, 132, 135, 145, 148, 154, 159, 164, 170, 176, 178, 190, 188, 193, 196, 208, 222, 224, 226, 230, 238, 238, 250, 250, 258, 264, 267, 272, 276
Offset: 1

Views

Author

Juri-Stepan Gerasimov, May 16 2010

Keywords

Crossrefs

Programs

  • Maple
    A023416 := proc(n) a := 0 ; for d in convert(n,base,2) do if d = 0 then a := a+1 ; end if; end do; a ; end proc:
    A035103 := proc(n) A023416(ithprime(n)) ; end proc:
    A177959 := proc(n) ithprime(n)-A035103(n) ; end proc:
    seq(A177959(n),n=1..120) ; # R. J. Mathar, May 30 2010

Formula

a(n) = A000040(n) - A035103(n).

Extensions

Corrected (39 removed, 124 replaced by 224, 126 replaced by 226) by R. J. Mathar, May 30 2010
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