A092951 - OEIS

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A092951

Beginning with n, add the next number, subtract the previous number, and so on; then a(n) is the largest prime arising in this process, or 0 if no prime is reached in 2n-1 steps: a(n) is the largest occurring prime in the sum n + (n+1) - (n-1) + (n+2) - (n-2) + (n+3) - (n-3) + ... +- 1 occurring at any stage.

3, 5, 7, 17, 19, 37, 37, 41, 67, 101, 103, 73, 107, 197, 199, 257, 257, 157, 263, 401, 401, 269, 487, 577, 577, 677, 677, 281, 787, 421, 787, 593, 907, 797, 1091, 1297, 1297, 1301, 1447, 1601, 1601, 1453, 1607, 1609, 1459

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OFFSET

1,1

COMMENTS

Conjecture: No term is zero.

LINKS

Table of n, a(n) for n=1..45.

EXAMPLE

a(5) = 19: the steps are 5, 5+6, 5+6-4, 5+6-4+7, 5+6-4+7-3, 5+6-4+7-3+8, 5+6-4+7-3+8-2, 5+6-4+7-3+8-2+9, 5+6-4+7-3+8-2+9-1, and the numbers arising are 5, 11, 7, 14, 11, 19, 17, 26, 25; 19 is the largest prime.

PROG

(GAP) A := function ( n ) local m, p, l, u; p := 0; u := n + 1; l := n - 1; m := n; if IsPrime( m ) then p := m; fi; repeat m := m + u; if IsPrime( m ) then p := m; fi; u := u + 1; m := m - l; if m > p and IsPrime( m ) then p := m; fi; l := l - 1; until l = 0; return p; end; # Simon Nickerson (simonn(AT)maths.bham.ac.uk), Jun 29 2005

CROSSREFS

Cf. A092950.

Sequence in context: A085499 A169628 A171254 * A001259 A248370 A087126

Adjacent sequences: A092948 A092949 A092950 * A092952 A092953 A092954

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Mar 24 2004

EXTENSIONS

More terms from Simon Nickerson (simonn(AT)maths.bham.ac.uk), Jun 29 2005

STATUS

approved