A085107 - OEIS

A085107

Starting with n-1 go on adding the numbers less than n and coprime to it in descending order until one gets a prime. a(n) = this prime, or 0 if no such number exists.

0, 0, 2, 3, 7, 5, 11, 7, 0, 19, 19, 11, 23, 13, 53, 0, 31, 17, 0, 19, 0, 101, 43, 23, 47, 131, 0, 139, 0, 29, 59, 31, 233, 223, 67, 179, 71, 37, 373, 109, 79, 41, 83, 43, 269, 457, 0, 47, 431, 139, 641, 313, 103, 53, 107, 251, 613, 643, 0, 59, 0, 61, 587, 0, 127, 521, 131, 67

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OFFSET

1,3

COMMENTS

a(p+1) = p, p is a prime.

If n is prime and 2n-3 is not prime, then a(n) = 0. - David Wasserman, Jan 27 2005

There are 105 zeros in the first 1000 terms. - Harvey P. Dale, Feb 24 2016

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

EXAMPLE

a(10) = 9 + 7 + 3 = 19.

MATHEMATICA

cp[n_]:=SelectFirst[Accumulate[Select[Range[n, 1, -1], CoprimeQ[ #, n]&]], PrimeQ]/._Missing->0; Array[cp, 70] (* The program uses the SelectFirst function from Mathematica version 10 *) (* Harvey P. Dale, Feb 24 2016 *)

CROSSREFS

Sequence in context: A159842 A085102 A087572 * A358242 A241082 A219789

Adjacent sequences: A085104 A085105 A085106 * A085108 A085109 A085110

KEYWORD

nonn

AUTHOR

Amarnath Murthy and Meenakshi Srikanth (menakan_s(AT)yahoo.com), Jul 04 2003

EXTENSIONS

More terms from David Wasserman, Jan 27 2005

STATUS

approved