A261305 - OEIS

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A261305

a(n+1) = abs(a(n) - gcd(a(n), 5*n+4)), u(1) = 1.

1, 0, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 89, 88, 77, 76, 75, 72, 71, 70, 69, 68, 67, 66, 65, 64, 63, 62, 61, 60, 59, 58, 57, 56, 55, 54, 53, 52, 51, 50, 49, 48, 47, 46, 45, 44, 43, 42, 41, 40, 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

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OFFSET

1,3

COMMENTS

It is conjectured that a(n) = 0 implies that 5n+4 = a(n+1) is prime for n > 2, cf. A186256. (This is the sequence {u(n)} mentioned there.)

LINKS

Table of n, a(n) for n=1..81.

EXAMPLE

a(2) = a(1) - gcd(a(1),5+4) = 1 - 1 = 0.

a(3) = |a(2) - gcd(a(2),5*2+4)| = 14.

a(19) = 88, thus a(20) = 88 - gcd(88, 5*19+4) = 88 - 11 = 77.

PROG