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A246717 Numbers of the form 2n - 1 such that A246702(n) = 2. 3
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

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

PROG

(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)))))))

CROSSREFS

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

Sequence in context: A048976 A088546 A265816 * A295706 A265792 A322669

Adjacent sequences:  A246714 A246715 A246716 * A246718 A246719 A246720

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Nov 15 2014

EXTENSIONS

Terms corrected by Antti Karttunen, Nov 15 2014

STATUS

approved

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Last modified January 28 13:29 EST 2020. Contains 331321 sequences. (Running on oeis4.)