OFFSET
1,1
COMMENTS
Terms ending with digit 5 (in decimal) are very rare, because terms of A123250 are rare.
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..10000
EXAMPLE
6 = 2*3 is present as 3 = 2 + 2^0.
15 = 3*5 is present as 5 = 3 + 2^1.
35 = 5*7 is present as 7 = 5 + 2^1.
PROG
(PARI)
A020639(n) = if(1==n, n, vecmin(factor(n)[, 1]));
isA261078(n) = { my(d); if(bigomega(n)!=2, return(0), d = (n/A020639(n)) - A020639(n); (d && !bitand(d, d-1))); };
i=0; n=0; while(i < 10000, n++; if(isA261078(n), i++; write("b261078.txt", i, " ", n)));
(Scheme, with Antti Karttunen's IntSeq-library)
(define A261078 (MATCHING-POS 1 1 (lambda (n) (and (= 2 (A001222 n)) (pow2? (- (A006530 n) (A020639 n)))))))
(define (pow2? n) (and (> n 0) (zero? (A004198bi n (- n 1))))) ;; A004198bi implements bitwise-AND (Cf. A004198)
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Sep 22 2015
STATUS
approved