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A120402
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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.
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OFFSET
| 1,1
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COMMENTS
| 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.
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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.
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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.
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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;
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CROSSREFS
| Cf. A119752, A119754, A119751, A119753, A103828.
Sequence in context: A053500 A080090 A125263 * A110073 A090256 A126140
Adjacent sequences: A120399 A120400 A120401 * A120403 A120404 A120405
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KEYWORD
| more,nonn
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AUTHOR
| Walter Kehowski (wkehowski(AT)cox.net), Jul 02 2006
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