A349487 a(n) = A132739((n-5)*(n+5)).

11, 24, 39, 56, 3, 96, 119, 144, 171, 8, 231, 264, 299, 336, 3, 416, 459, 504, 551, 24, 651, 704, 759, 816, 7, 936, 999, 1064, 1131, 48, 1271, 1344, 1419, 1496, 63, 1656, 1739, 1824, 1911, 16, 2091, 2184, 2279, 2376, 99, 2576, 2679, 2784, 2891, 24, 3111

Offset

6,1

Comments

Shares 614 initial terms with A061043. First difference is A061043(620)=615 vs. a(620)=123.

Links

Table of n, a(n) for n=6..56.

Formula

a(n) = A132739(A098603(n-5)).

Example

a(9)  = A132739(( 9-5)*( 9+5)) = A132739(56) = 56,
a(10) = A132739((10-5)*(10+5)) = A132739(75) = 3,
a(11) = A132739((11-5)*(11+5)) = A132739(96) = 96.

Mathematica

Table[Last@Select[Divisors[(n - 5)*(n + 5)], Mod[#, 5] != 0 &], {n, 6,
   56}] (* Giorgos Kalogeropoulos, Nov 19 2021 *)
Table[(n - 5)*(n + 5)/5^IntegerExponent[(n - 5)*(n + 5), 5], {n, 6, 56}] (* Amiram Eldar, Nov 22 2021 *)

Prog

(PARI) A132739(n)=n/5^valuation(n, 5);
a(n) = A132739((n-5)*(n+5));
[a(n)|n<-[6..25]]
(Ruby) p (6..25).map { |n| x = (n-5)*(n+5); x /= 5 while (x % 5) == 0; x }
(Python)
def A349487(n):
    a, b = divmod(n*n-25, 5)
    while b == 0:
        a, b = divmod(a, 5)
    return 5*a+b # Chai Wah Wu, Dec 05 2021

Crossrefs

Cf. A061043, A098603, A132739.

Sequence in context: A213062 A157756 A061043 * A098603 A274620 A053061

Adjacent sequences: A349484 A349485 A349486 * A349488 A349489 A349490

Keyword

nonn

Author

Simon Strandgaard, Nov 19 2021

Status

approved