A261307 a(n+1) = abs(a(n) - gcd(a(n), 7*n+6)), a(1) = 1.
1, 0, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 167, 166, 165, 164, 163, 162, 161, 160, 159, 158, 79, 78, 77, 76, 75, 74, 73, 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
Offset: 1
Keywords
Examples
a(2) = a(1) - gcd(a(1),7+6) = 1 - 1 = 0. a(3) = |a(2) - gcd(a(2),7*2+6)| = gcd(0,17) = 17 is prime. a(33) = 158, thus a(6) = 158 - gcd(158,7*33+6) = 158 - 79 = 79.
Links
- Harvey P. Dale, Table of n, a(n) for n = 1..1000
Programs
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Mathematica
nxt[{n_,a_}]:={n+1,Abs[a-GCD[a,7n+6]]}; NestList[nxt,{1,1},80][[All,2]] (* Harvey P. Dale, Apr 26 2017 *) -
PARI
print1(a=1);for(n=1,99,print1(",",a=abs(a-gcd(a,7*n+6))))
Comments