|
Search: id:A120402
|
|
|
| A120402 |
|
a(1)=2; a(n)=first even number greater than a(n-1) such that 2*a(n)-1 is prime and a(i)+a(n)-1 is prime for all 1<=i<=n-1. |
|
+0
1
|
|
| 2, 4, 10, 70, 430, 4090, 86530, 513100, 913570, 7914340
(list; graph; listen)
|
|
|
OFFSET
|
1,1
|
|
|
COMMENT
|
All elements after the first are 4 mod 6. In base 12 the sequence is 2, 4, X, 5X, 2EX, 244X, 420XX, 208E24, 38082X, 2798084, where X is 10 and E is eleven.
|
|
FORMULA
|
a(1)=2; a(n) = s where s is the first even number s>a(n-1) such that 2*s-1 is prime and s+a(i)-1 is prime, 1<=i<=n-1.
|
|
EXAMPLE
|
a(2)=4 since 4 is the first even number > a(1)=2 such that 2*4-1=7 is prime and 4+2-1=5 is prime.
|
|
MAPLE
|
EP:=[2]: for w to 1 do for k from 0 to 12^8 do n:=6*k+4; p:=2*n-1; Q:=map(z-> z+n-1, EP); if isprime(p) and andmap(isprime, Q) then EP:=[op(EP), n]; print(n); fi od od;
|
|
CROSSREFS
|
Cf. A119752, A119754, A119751, A119753, A103828.
Sequence in context: A053500 A080090 A125263 this_sequence A110073 A090256 A126140
Adjacent sequences: A120399 A120400 A120401 this_sequence A120403 A120404 A120405
|
|
KEYWORD
|
easy,more,nonn
|
|
AUTHOR
|
Walter Kehowski (wkehowski(AT)cox.net), Jul 02 2006
|
|
|
Search completed in 0.002 seconds
|
