A086712 Number of times the n-th prime power can be written as an arithmetic mean of two other prime powers.

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

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