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A088948 (A006530(x)+A020639(x))/2 is an integer; that is, arithmetic mean of least and largest prime factor is an integer. 3
2, 3, 4, 5, 7, 8, 9, 11, 13, 15, 16, 17, 19, 21, 23, 25, 27, 29, 31, 32, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 64, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99, 101, 103, 105, 107, 109, 111, 113, 115, 117, 119, 121, 123, 125 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Union of odd numbers and powers of 2 minus {1}. - Ivan Neretin, Dec 30 2015

LINKS

Michael De Vlieger, Table of n, a(n) for n = 1..10000

EXAMPLE

Primes and prime powers are here.

Also other composites: n=105, (3+7)/2=5 is an integer moreover divides n.

MATHEMATICA

Rest@ Select[Range@ 125, IntegerQ[(FactorInteger[#][[1, 1]] + FactorInteger[#][[-1, 1]])/2] &] (* Michael De Vlieger, Mar 28 2015 *)

PROG

(PARI) is_a088948(n) = {local (f); f=factor(n); if(Mod(vecmin(f[, 1])+vecmax(f[, 1]), 2)==0, 1, 0)} \\ Michael B. Porter, Mar 28 2015

CROSSREFS

Different from A046687.

Cf. A006530, A020639, A088949, A088949, A046687.

Sequence in context: A078174 A174894 A275616 * A115405 A257144 A316476

Adjacent sequences:  A088945 A088946 A088947 * A088949 A088950 A088951

KEYWORD

nonn

AUTHOR

Labos Elemer, Nov 20 2003

STATUS

approved

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Last modified August 19 08:17 EDT 2019. Contains 326115 sequences. (Running on oeis4.)