OFFSET
1,2
COMMENTS
EXAMPLE
7 is included, because it is a prime, and repunit in base-2: '111'.
10 is included, as 10=2*5, and when we add 2 ('10' in binary) and 5 ('101' in binary), we also get 7 ('111' in binary), without producing any carries.
PROG
(Scheme, with Antti Karttunen's IntSeq-library)
(define A235490 (MATCHING-POS 1 1 (lambda (n) (or (= 1 n) (and (= (A001414 n) (A072593 n)) (pow2? (1+ (A001414 n))))))))
(define (pow2? n) (let loop ((n n) (i 0)) (cond ((zero? n) #f) ((odd? n) (and (= 1 n) i)) (else (loop (/ n 2) (1+ i))))))
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Antti Karttunen, Jan 22 2014
STATUS
approved