A391075 a(n) = 25*n+1 if n is odd and floor((n+6)/8) if n is even.

0, 26, 1, 76, 1, 126, 1, 176, 1, 226, 2, 276, 2, 326, 2, 376, 2, 426, 3, 476, 3, 526, 3, 576, 3, 626, 4, 676, 4, 726, 4, 776, 4, 826, 5, 876, 5, 926, 5, 976, 5, 1026, 6, 1076, 6, 1126, 6, 1176, 6, 1226, 7, 1276, 7, 1326, 7, 1376, 7, 1426, 8, 1476, 8, 1526, 8, 1576, 8, 1626, 9, 1676, 9, 1726, 9, 1776, 9, 1826, 10

Offset

0,2

Comments

Does iterating n -> a(n) always reach 1 (i.e., the cycle 1 -> 26 -> 4 -> 1)?

Links

Table of n, a(n) for n=0..74.

Index entries for linear recurrences with constant coefficients, signature (0,1,0,0,0,0,0,1,0,-1).

Formula

a(2*n+1) = a(2*n-1) + 50 for n > 0.

a(8*n) = a(8*n-2) = a(8*n-4) = a(8*n-6) for n > 0.

a(n) = a(n-2) + a(n-8) - a(n-10).

G.f.: (26*x + x^2 + 50*x^3 + 50*x^5 + 50*x^7 + 24*x^9) / ((1-x^2) * (1-x^8)).

Mathematica

a[n_] := If[OddQ[n], 25*n + 1, Floor[(n + 6)/8]]; Array[a, 100, 0] (* Amiram Eldar, Nov 27 2025 *)

Prog

(PARI) a(n) = if(n%2==0, floor((n+6)/8), 25*n+1)
(Python)
def A391075(n): return 25*n+1 if n&1 else n+6>>3 # Chai Wah Wu, Nov 30 2025

Crossrefs

Cf. A006370, A391054.

Sequence in context: A040700 A070614 A040701 * A050459 A040669 A040668

Adjacent sequences: A391072 A391073 A391074 * A391076 A391077 A391078

Keyword

nonn,easy

Author

Werner Schulte, Nov 27 2025

Status

approved