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A120450 Number of ways to express a prime p as 2*p1 + 3*p2, where p1, p2 are primes or 1. 1
0, 0, 1, 1, 1, 2, 2, 2, 2, 2, 2, 3, 3, 4, 3, 3, 3, 5, 4, 4, 4, 4, 4, 4, 6, 3, 5, 4, 4, 4, 6, 5, 5, 5, 5, 7, 5, 6, 6, 6, 6, 7, 5, 6, 7, 6, 7, 9, 8, 8, 6, 7, 7, 8, 7, 9, 6, 10 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

COMMENTS

It seems that every prime p > 3 can be expressed as 2*p1 + 3*p2, where p1, p2 are primes or 1. I have tested it for the first 1500 primes (up to 12553) and it is true.

LINKS

Table of n, a(n) for n=1..58.

EXAMPLE

a(11)=2 because we can write 31 (the 11th prime) as 2* 5 + 3* 7 OR 2* 11 + 3* 3

a(12)=3 because we can write 37 (the 12th prime) as 2* 2 + 3* 11 OR 2* 11 + 3* 5 OR 2* 17 + 3* 1

CROSSREFS

Sequence in context: A030603 A092670 A210528 * A127238 A072114 A090621

Adjacent sequences:  A120447 A120448 A120449 * A120451 A120452 A120453

KEYWORD

nonn

AUTHOR

Vassilis Papadimitriou, Jul 20 2006

STATUS

approved

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Last modified September 29 18:27 EDT 2020. Contains 337432 sequences. (Running on oeis4.)