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 11 results. Next

A155578 Intersection of A000404 and A155717: N = a^2 + b^2 = c^2 + 7*d^2 for some positive integers a,b,c,d.

Original entry on oeis.org

8, 29, 32, 37, 53, 72, 109, 113, 116, 128, 137, 148, 149, 193, 197, 200, 212, 232, 233, 261, 277, 281, 288, 296, 317, 333, 337, 373, 389, 392, 400, 401, 421, 424, 436, 449, 452, 457, 464, 477, 512, 541, 548, 557, 569, 592, 596, 613, 617, 641, 648, 653, 673
Offset: 1

Views

Author

M. F. Hasler, Jan 25 2009

Keywords

Comments

Subsequence of A155568 (where a,b,c,d may be zero).

Crossrefs

Cf. A000404, A154777, A092572, A097268, A154778, A155716, A155717.

Programs

  • PARI
    isA155578(n,/* optional 2nd arg allows us to get other sequences */c=[7,1]) = { for(i=1,#c, for(b=1,sqrtint((n-1)\c[i]), issquare(n-c[i]*b^2) & next(2)); return);1}
for( n=1,999, isA155578(n) & print1(n","))
  • Python
    from math import isqrt
def aupto(limit):
    cands = range(1, isqrt(limit)+1)
    left =  set(a**2 +   b**2 for a in cands for b in cands)
    right = set(c**2 + 7*d**2 for c in cands for d in cands)
    return sorted(k for k in left & right if k <= limit)
print(aupto(673)) # Michael S. Branicky, Aug 29 2021

A155711 Intersection of A154777 and A155717: N = a^2 + 2b^2 = c^2 + 7d^2 for some positive integers a,b,c,d.

Original entry on oeis.org

11, 43, 44, 67, 72, 88, 99, 107, 113, 121, 137, 144, 163, 172, 176, 179, 193, 211, 233, 268, 275, 281, 288, 331, 337, 344, 347, 352, 379, 387, 396, 401, 428, 443, 449, 452, 457, 473, 484, 491, 499, 536, 539, 547, 548, 569, 571, 576, 603, 617, 641, 648, 652
Offset: 1

Views

Author

M. F. Hasler, Jan 25 2009

Keywords

Crossrefs

Cf. A000404, A154777, A092572, A097268, A154778, A155716, A155717, A155560-A155578.

Programs

  • PARI
    isA155711(n,/* optional 2nd arg allows us to get other sequences */c=[7,2]) = { for(i=1,#c, for(b=1,sqrtint((n-1)\c[i]), issquare(n-c[i]*b^2) & next(2)); return);1}
for( n=1,999, isA155711(n) & print1(n","))

A155716 Numbers of the form N = a^2 + 6b^2 for some positive integers a,b.

Original entry on oeis.org

7, 10, 15, 22, 25, 28, 31, 33, 40, 42, 49, 55, 58, 60, 63, 70, 73, 79, 87, 88, 90, 97, 100, 103, 105, 106, 112, 118, 121, 124, 127, 132, 135, 145, 150, 151, 154, 159, 160, 166, 168, 175, 177, 186, 193, 196, 198, 199, 202, 214, 217, 220, 223, 225, 231, 232, 240
Offset: 1

Views

Author

M. F. Hasler, Jan 25 2009

Keywords

Comments

Subsequence of A002481 (which allows for a and b to be zero).
Primes are in A033199. - Bernard Schott, Sep 20 2019

Links

Crossrefs

Cf. A002481, A033199.
Cf. A000404, A154777, A092572, A097268, A154778, A155707-A155717, A155560-A155578.

Programs

  • Mathematica
    With[{upto=240},Select[Union[#[[1]]^2+6#[[2]]^2&/@Tuples[ Range[Sqrt[ upto]], 2]],#<=upto&]] (* Harvey P. Dale, Aug 05 2016 *)
  • PARI
    isA155716(n,/* optional 2nd arg allows us to get other sequences */c=6) = { for(b=1,sqrtint((n-1)\c), issquare(n-c*b^2) & return(1))}
for( n=1,999, isA155716(n) & print1(n","))
  • PARI
    upto(n) = my(res=List()); for(i=1,sqrtint(n),for(j=1, sqrtint((n - i^2) \ 6), listput(res, i^2 + 6*j^2))); listsort(res,1); res \\ David A. Corneth, Sep 18 2019

A216511 Number of positive integer solutions to the equation a^2 + 7*b^2 = n.

Original entry on oeis.org

0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 2, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0
Offset: 1

Views

Author

V. Raman, Sep 08 2012

Keywords

Crossrefs

Cf. A155717.

Programs

  • Mathematica
    r[n_] := Reduce[x > 0 && y > 0 && x^2 + 7 y^2 == n, Integers];
a[n_] := Which[rn = r[n]; rn === False, 0, Head[rn] === And, 1, Head[rn] === Or, Length[rn], True, -1];
Table[a[n], {n, 1, 87}] (* Jean-François Alcover, Jun 24 2017 *)

A155712 Intersection of A092572 and A155716: N = a^2 + 3b^2 = c^2 + 6d^2 for some positive integers a,b,c,d.

Original entry on oeis.org

7, 28, 31, 49, 63, 73, 79, 97, 100, 103, 112, 124, 127, 151, 175, 193, 196, 199, 217, 223, 241, 252, 271, 279, 292, 313, 316, 337, 343, 367, 388, 400, 409, 412, 433, 439, 441, 448, 457, 463, 484, 487, 496, 508, 511, 553, 567, 577, 601, 604, 607, 631, 657, 673
Offset: 1

Views

Author

M. F. Hasler, Jan 25 2009

Keywords

Comments

From Robert Israel, Jan 19 2025: (Start)
If k is a term, then so is j^2 * k for all positive integers j.
The primes in this sequence appear to be A033199.
(End)

Links

Crossrefs

Cf. A000404, A033199, A092572, A097268, A154777, A154778, A155716, A155717, A155560-A155578.

Programs

  • Maple
    N:= 1000: # for terms <= N
A:= {seq(seq(a^2 + 3*b^2, b=1 .. floor(sqrt((N-a^2)/3))),a=1..floor(sqrt(N)))}
   intersect {seq(seq(c^2 + 6*d^2, d = 1 .. floor(sqrt((N-c^2)/6))),c=1..floor(sqrt(N)))}:
sort(convert(A,list)); # Robert Israel, Jan 19 2025
  • PARI
    isA155712(n,/* optional 2nd arg allows to get other sequences */c=[6,3]) = { for(i=1,#c, for(b=1,sqrtint((n-1)\c[i]), issquare(n-c[i]*b^2) && next(2)); return);1}
for( n=1,999, isA155712(n) && print1(n",")) \\ Update to modern PARI syntax (& -> &&) by M. F. Hasler, Jan 18 2025

A155574 Intersection of A154777 and A092572: N = a^2 + 2b^2 = c^2 + 3d^2 for some positive integers a,b,c,d.

Original entry on oeis.org

12, 19, 36, 43, 48, 57, 67, 73, 76, 97, 108, 129, 139, 144, 147, 163, 171, 172, 192, 193, 201, 211, 219, 228, 241, 268, 283, 291, 292, 300, 304, 307, 313, 324, 331, 337, 361, 379, 387, 388, 409, 417, 432, 433, 441, 457, 475, 484, 489, 499, 507, 513, 516, 523
Offset: 1

Views

Author

M. F. Hasler, Jan 25 2009

Keywords

Comments

Subsequence of A155564 (where a,b,c,d may be zero).

Crossrefs

Cf. A000404, A154777, A092572, A097268, A154778, A155716, A155717, A155560-A155578.

Programs

  • PARI
    isA155574(n,/* optional 2nd arg allows us to get other sequences */c=[3,2]) = { for(i=1,#c, for(b=1,sqrtint((n-1)\c[i]), issquare(n-c[i]*b^2) & next(2)); return);1}
for( n=1,999, isA155574(n) & print1(n","))

A155575 Intersection of A000404 and A154778: N = a^2 + b^2 = c^2 + 5d^2 for some positive integers a,b,c,d.

Original entry on oeis.org

29, 41, 45, 61, 89, 101, 109, 116, 145, 149, 164, 180, 181, 205, 225, 229, 241, 244, 245, 261, 269, 281, 305, 349, 356, 369, 389, 401, 404, 405, 409, 421, 436, 445, 449, 461, 464, 505, 509, 521, 541, 545, 549, 569, 580, 596, 601, 641, 656, 661, 701, 709, 720
Offset: 1

Views

Author

M. F. Hasler, Jan 25 2009

Keywords

Comments

Subsequence of A155565 (where a,b,c,d may be zero).

Crossrefs

Cf. A000404, A154777, A092572, A097268, A154778, A155716, A155717, A155560-A155578.

Programs

  • PARI
    isA155575(n,/* optional 2nd arg allows us to get other sequences */c=[5,1]) = { for(i=1,#c, for(b=1,sqrtint((n-1)\c[i]), issquare(n-c[i]*b^2) & next(2)); return);1}
for( n=1,999, isA155575(n) & print1(n","))

A155571 Intersection of A000404, A092572 and A154778: N = a^2 + b^2 = c^2 + 3d^2 = e^2 + 5f^2 for some positive integers a,b,c,d,e,f.

Original entry on oeis.org

61, 109, 181, 229, 241, 244, 349, 409, 421, 436, 541, 549, 601, 661, 709, 724, 769, 829, 900, 916, 964, 976, 981, 1009, 1021, 1069, 1129, 1201, 1225, 1249, 1321, 1381, 1396, 1429, 1489, 1521, 1525, 1549, 1609, 1621, 1629, 1636, 1669, 1684, 1741, 1744, 1789
Offset: 1

Views

Author

M. F. Hasler, Jan 25 2009

Keywords

Crossrefs

Cf. A000404, A154777, A092572, A097268, A154778, A155716, A155717, A155560-A155578.

Programs

  • PARI
    isA155571(n,/* optional 2nd arg allows us to get other sequences */c=[5,3,1]) = { for(i=1,#c, for(b=1,sqrtint((n-1)\c[i]), issquare(n-c[i]*b^2) & next(2)); return);1}
for( n=1,1999, isA155571(n) & print1(n","))

A155572 Intersection of A000404, A154777 and A154778: N = a^2 + b^2 = c^2 + 2d^2 = e^2 + 5f^2 for some positive integers a,b,c,d,e,f.

Original entry on oeis.org

41, 89, 164, 225, 241, 281, 356, 369, 401, 409, 449, 521, 569, 601, 641, 656, 761, 769, 801, 809, 881, 900, 929, 964, 1009, 1025, 1049, 1124, 1129, 1201, 1249, 1289, 1321, 1361, 1409, 1424, 1476, 1481, 1489, 1521, 1601, 1604, 1609, 1636, 1681, 1721, 1796
Offset: 1

Views

Author

M. F. Hasler, Jan 25 2009

Keywords

Crossrefs

Cf. A000404, A154777, A092572, A097268, A154778, A155716, A155717, A155560-A155578.

Programs

  • PARI
    isA155572(n,/* optional 2nd arg allows us to get other sequences */c=[5,2,1]) = { for(i=1,#c, for(b=1,sqrtint((n-1)\c[i]), issquare(n-c[i]*b^2) & next(2)); return);1}
for( n=1,1999, isA155572(n) & print1(n","))

A155573 Intersection of A000404, A154777 and A092572: N = a^2 + b^2 = c^2 + 2d^2 = e^2 + 3f^2 for some positive integers a,b,c,d,e,f.

Original entry on oeis.org

73, 97, 193, 241, 292, 313, 337, 388, 409, 433, 457, 577, 601, 657, 673, 769, 772, 873, 900, 937, 964, 1009, 1033, 1129, 1153, 1156, 1168, 1201, 1249, 1252, 1297, 1321, 1348, 1489, 1521, 1552, 1609, 1636, 1657, 1732, 1737, 1753, 1777, 1801, 1825, 1828
Offset: 1

Views

Author

M. F. Hasler, Jan 25 2009

Keywords

Crossrefs

Cf. A000404, A154777, A092572, A097268, A154778, A155716, A155717, A155560-A155578.

Programs

  • PARI
    isA155573(n,/* optional 2nd arg allows us to get other sequences */c=[3,2,1]) = { for(i=1,#c, for(b=1,sqrtint((n-1)\c[i]), issquare(n-c[i]*b^2) & next(2)); return);1}
for( n=1,1999, isA155573(n) & print1(n","))
Showing 1-10 of 11 results. Next

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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