A261304 a(n+1) = abs(a(n) - gcd(a(n), 4n+3)), a(1) = 1.

1, 0, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 59, 58, 57, 56, 55, 54, 53, 52, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 251, 250, 249, 248, 247, 246, 245, 244, 243, 242, 241, 240, 239, 238, 237, 236

Offset: 1

Author

M. F. Hasler, Aug 14 2015

Keywords

• nonn

Comments

The absolute value is relevant only when a(n) = 0, in which case a(n+1) = gcd(a(n), 4n+3) = 4n+3.

It is conjectured that a(n) = 0 implies that 4n+3 = a(n+1) is prime, cf. A186256. (This is the sequence {u(n)} mentioned there.)

Crossrefs

Cf. A261301 - A261310, A186253 - A186263, A106108.

Programs

PARI

print1(a=1);for(n=1,199,print1(",",a=abs(a-gcd(a,4*n+3))))