A086712 - OEIS

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A086712

Number of times the n-th prime power can be written as an arithmetic mean of two other prime powers.

0

0, 1, 2, 2, 3, 3, 3, 4, 3, 4, 6, 6, 5, 5, 7, 8, 5, 6, 6, 7, 6, 8, 6, 8, 8, 7, 8, 10, 10, 9, 8, 9, 14, 8, 10, 11, 10, 12, 8, 11, 8, 12, 13, 12, 11, 11, 13, 13, 13, 13, 13, 11, 11, 14, 11, 13, 16, 12, 16, 14, 15, 16, 17, 13, 16, 15, 12, 18, 27, 15, 19, 18, 17, 15, 16, 15, 13, 18, 17, 15

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OFFSET

1,3

LINKS

Table of n, a(n) for n=1..80.

Eric Weisstein's World of Mathematics, Prime Power

EXAMPLE

n=7, A000961(7)=8=2^3: (3+13)/2=(A000961(3)+A000961(10))/2, (5+11)/2=(A000961(5)+A000961(9))/2 and (7+3^2)/2=(A000961(6)+A000961(8))/2: therefore a(7)=3.

CROSSREFS

Cf. A000961, A071681.

Sequence in context: A000121 A230022 A049846 * A125842 A029865 A211190

Adjacent sequences: A086709 A086710 A086711 * A086713 A086714 A086715

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Aug 01 2003

STATUS

approved