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A122478 Minimum number k>0 such that ((2n+1)^k - (2n-1)^k)/2 is prime. 2
3, 13, 3, 3, 5, 3, 17, 3, 163, 3, 3, 109, 3, 13, 19, 5, 3, 3, 1879, 3, 13, 379, 7, 1531, 7, 5, 337, 5, 3, 61, 19, 3, 23, 3, 11, 16417, 163, 23, 3, 5, 3, 3, 3, 5 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All a(n) are primes. Corresponding minimal primes of the form ((2n+1)^k - (2n-1)^k)/2 are {13, 609554401, 109, 193, 51001, 433, 44937854708156010721, 769, ...}.

a(46)-a(49) are 17, 5, 31, 3. a(51)-a(61) are 109, 5, 7, 89, 13, 3, 31, 53, 5, 3, 5. a(63)-a(69) are 3, 7, 19, 5, 167, 163, 293. a(71)-a(74) are 3, 3407, 3, 3. a(76)-a(77) are 3, 19.

a(45), a(50), a(62), a(70), a(75) are currently unknown.

a(45) > 30000. [From Max Alekseyev, May 18 2010]

LINKS

Table of n, a(n) for n=1..44.

CROSSREFS

Cf. A028491, A121877.

Sequence in context: A010258 A107774 A253685 * A164558 A128368 A050089

Adjacent sequences:  A122475 A122476 A122477 * A122479 A122480 A122481

KEYWORD

hard,more,nonn

AUTHOR

Alexander Adamchuk, Sep 14 2006, Sep 17 2006, Oct 07 2006

EXTENSIONS

a(36)=16417 from Max Alekseyev, May 11 2010

STATUS

approved

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Last modified September 23 12:43 EDT 2021. Contains 347617 sequences. (Running on oeis4.)