A088949 Composite numbers k such that (A006530(k) + A020639(k))/2 is an integer that divides k; special terms of A088948.

4, 8, 9, 16, 25, 27, 32, 49, 64, 81, 105, 121, 125, 128, 169, 231, 243, 256, 289, 315, 343, 361, 512, 525, 529, 625, 627, 693, 729, 735, 841, 897, 935, 945, 961, 1024, 1155, 1331, 1369, 1575, 1581, 1617, 1681, 1729, 1849, 1881, 2048, 2079, 2187, 2197, 2205, 2209

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

k = 315 = 3*3*5*7 (composite); (3 + 7)/2 = 5, which divides k.

Mathematica

q[k_] := CompositeQ[k] && Module[{p = FactorInteger[k][[;; , 1]], m}, m = (p[[1]] + p[[-1]]); EvenQ[m] && Divisible[k, m/2]]; Select[Range[2500], q] (* Amiram Eldar, Mar 01 2025 *)

Prog

(PARI) lista(nn) = {forcomposite(n=1, nn, my(f = factor(n)[, 1], x = (vecmin(f) + vecmax(f))/2); if ((denominator(x)==1) && !(n % x), print1(n, ", ")); ); } \\ Michel Marcus, Jul 09 2018

Crossrefs

Cf. A006530, A020639, A088948, A088595, A046687.

Sequence in context: A377819 A306531 A363722 * A134600 A134601 A227476

Adjacent sequences: A088946 A088947 A088948 * A088950 A088951 A088952

Keyword

nonn,changed

Author

Labos Elemer, Nov 20 2003

Extensions

Edited by Jon E. Schoenfield, Jul 08 2018

More terms from Michel Marcus, Jul 09 2018

Status

approved