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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A253240 Square array read by antidiagonals: T(m, n) = Phi_m(n), the m-th cyclotomic polynomial at x=n.

Original entry on oeis.org

1, 1, -1, 1, 0, 1, 1, 1, 2, 1, 1, 2, 3, 3, 1, 1, 3, 4, 7, 2, 1, 1, 4, 5, 13, 5, 5, 1, 1, 5, 6, 21, 10, 31, 1, 1, 1, 6, 7, 31, 17, 121, 3, 7, 1, 1, 7, 8, 43, 26, 341, 7, 127, 2, 1, 1, 8, 9, 57, 37, 781, 13, 1093, 17, 3, 1, 1, 9, 10, 73, 50, 1555, 21, 5461, 82, 73, 1, 1, 1, 10, 11, 91, 65, 2801, 31, 19531, 257, 757, 11, 11, 1, 1, 11, 12, 111, 82, 4681, 43, 55987, 626, 4161, 61, 2047, 1, 1
Offset: 0

Views

Author

Eric Chen, Apr 22 2015

Keywords

Comments

Outside of rows 0, 1, 2 and columns 0, 1, only terms of A206942 occur.
Conjecture: There are infinitely many primes in every row (except row 0) and every column (except column 0), the indices of the first prime in n-th row and n-th column are listed in A117544 and A117545. (See A206864 for all the primes apart from row 0, 1, 2 and column 0, 1.)
Another conjecture: Except row 0, 1, 2 and column 0, 1, the only perfect powers in this table are 121 (=Phi_5(3)) and 343 (=Phi_3(18)=Phi_6(19)).

Examples

			Read by antidiagonals:
m\n  0   1   2   3   4   5   6   7   8   9  10  11  12
------------------------------------------------------
0    1   1   1   1   1   1   1   1   1   1   1   1   1
1   -1   0   1   2   3   4   5   6   7   8   9  10  11
2    1   2   3   4   5   6   7   8   9  10  11  12  13
3    1   3   7  13  21  31  43  57  73  91 111 133 157
4    1   2   5  10  17  26  37  50  65  82 101 122 145
5    1   5  31 121 341 781 ... ... ... ... ... ... ...
6    1   1   3   7  13  21  31  43  57  73  91 111 133
etc.
The cyclotomic polynomials are:
n        n-th cyclotomic polynomial
0        1
1        x-1
2        x+1
3        x^2+x+1
4        x^2+1
5        x^4+x^3+x^2+x+1
6        x^2-x+1
...
		

Crossrefs

Main diagonal is A070518.
Indices of primes in n-th column for n = 1-10 are A246655, A072226, A138933, A138934, A138935, A138936, A138937, A138938, A138939, A138940.
Indices of primes in main diagonal is A070519.
Cf. A117544 (indices of first prime in n-th row), A085398 (indices of first prime in n-th row apart from column 1), A117545 (indices of first prime in n-th column).
Cf. A206942 (all terms (sorted) for rows>2 and columns>1).
Cf. A206864 (all primes (sorted) for rows>2 and columns>1).

Programs

  • Mathematica
    Table[Cyclotomic[m, k-m], {k, 0, 49}, {m, 0, k}]
  • PARI
    t1(n)=n-binomial(floor(1/2+sqrt(2+2*n)), 2)
    t2(n)=binomial(floor(3/2+sqrt(2+2*n)), 2)-(n+1)
    T(m, n) = if(m==0, 1, polcyclo(m, n))
    a(n) = T(t1(n), t2(n))

Formula

T(m, n) = Phi_m(n)

A252502 Number of digits of Phi_n(10), or number of digits in base b of Phi_n(b), where Phi is the cyclotomic polynomial.

Original entry on oeis.org

1, 2, 3, 3, 5, 2, 7, 5, 7, 4, 11, 4, 13, 6, 8, 9, 17, 6, 19, 8, 12, 10, 23, 8, 21, 12, 19, 12, 29, 9, 31, 17, 20, 16, 24, 12, 37, 18, 24, 16, 41, 13, 43, 20, 24, 22, 47, 16, 43, 20, 32, 24, 53, 18, 40, 24, 36, 28, 59, 17, 61, 30, 36, 33, 48, 21, 67, 32, 44, 25, 71, 24
Offset: 1

Views

Author

Eric Chen, Dec 17 2014

Keywords

Comments

a(n) = phi(n) if and only if the number of distinct prime factors of n (A001221(n)) is even, a(n) = phi(n) + 1 if and only if the number of distinct prime factors of n (A001221(n)) is odd, where phi is Euler's totient function.

Examples

			Values of phi_n(b) written in base b are #, 11, 111, 101, 11111, #1, 1111111, 10001, 1001001, #0#1, 11111111111, ##01, ..., where # represents b - 1.
		

Crossrefs

Programs

  • Mathematica
    a252502[n_] := Array[Total@DigitCount[Cyclotomic[#, 10]] &, n]; a252502[72] (* Michael De Vlieger, Dec 21 2014 *)
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