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Smallest prime p, such that either |A000040(n)-p| or A000040(n)+p is of the form 2^k.
4

%I #5 Mar 31 2012 13:21:16

%S 2,2,3,3,3,3,13,3,7,3,23,5,23,11,17,11,5,3,3,7,41,47,19,73,31,37,71,

%T 43,19,97,131,3,73,11,107,23,29,131,89,83,163,53,127,191,59,71,83,191,

%U 29,101,23,17,113,5,193,7,13,239,149,277,229,37,179,307,199,61,181,353,283

%N Smallest prime p, such that either |A000040(n)-p| or A000040(n)+p is of the form 2^k.

%H Ray Chandler, <a href="/A130971/b130971.txt">Table of n, a(n) for n=1..10000</a>

%o (Scheme:) (define (A130971 n) (let ((p1 (A000040 n))) (let loop ((i 1) (p2 2)) (cond ((pow2? (abs (- p1 p2))) p2) ((pow2? (+ p1 p2)) p2) (else (loop (+ i 1) (A000040 (+ i 1))))))))

%o (define (pow2? n) (and (> n 0) (zero? (A004198bi n (- n 1)))))

%Y Cf. A130971, A130972, A103150.

%K nonn

%O 1,1

%A _Antti Karttunen_, Jun 19 2007

%E Extended by _Ray Chandler_, Aug 06 2010