A246717 Numbers of the form 2n - 1 such that A246702(n) = 2.

7, 17, 23, 35, 41, 47, 49, 71, 77, 79, 95, 97, 103, 115, 137, 143, 167, 175, 191, 193, 199, 209, 235, 239, 245, 263, 271, 289, 295, 299, 311, 313, 319, 335, 343, 359, 367, 371, 383, 395, 401, 407, 409, 413, 415, 437, 449, 463, 475, 479, 487, 503, 515, 517, 521, 529, 535, 539, 551, 569, 575, 581, 583, 599, 607, 611, 647, 649, 667, 695, 707

Offset: 1

Author

Juri-Stepan Gerasimov, Nov 15 2014

Keywords

• nonn

Comments

From Antti Karttunen, Nov 15 2014: (Start)

Equally: Odd numbers n for which A246702((n+1)/2) = 2.

Primes in this sequence: 7, 17, 23, 41, 47, 71, 79, ... seem to be A115591.

A249819 gives the composite terms.

(End)

Links

• Antti Karttunen, Table of n, a(n) for n = 1..105

Crossrefs

Cf. A002326, A115591, A249819, A167791, A246702.

Programs

PARI

isA246717(n) = { if(!(n%2), return(0), my(u, s=0); u = n^2; for(k=1, u-1, if(!(((2^k)-1)%u), s++;if(s > 2, return(0)))); return(2==s)); }
n = 0; i = 0; while(i < 105, n++; if(isA246717(n), i++; write("b246717.txt", i, " ", n))); \\ From Antti Karttunen, Nov 15 2014
(Scheme, with Antti Karttunen's IntSeq-library)
(define A246717 (MATCHING-POS 1 1 (lambda (n) (and (odd? n) (= 2 (A246702 (/ (+ 1 n) 2)))))))

Extensions

Terms corrected by Antti Karttunen, Nov 15 2014