A273403 - OEIS

A273403

Numbers k such that (10^k - 7^k)/3 is prime.

2, 31, 103, 617, 10253, 10691, 35353, 129587, 556441 (list; graph; refs; listen; history; text; internal format)

	OFFSET	`1,1`
	COMMENTS	`All terms are prime.` `The corresponding primes: 17, 3333280741539321718064461652419, ...`
	LINKS	`Table of n, a(n) for n=1..9.` `Jon Grantham and Andrew Granville, Fibonacci primes, primes of the form 2^n-k and beyond, arXiv:2307.07894 [math.NT], 2023.`
	MATHEMATICA	`Select[Range[1, 10000], PrimeQ[(10^# - 7^#)/3] &]`
	PROG	`(PARI) for(n=1, 10000, if(isprime((10^n - 7^n)/3), print1(n, ", ")))`
	CROSSREFS	`Cf. A004023, A128026, A062576.` `Sequence in context: A243472 A336788 A107170 * A291052 A267888 A229014` `Adjacent sequences: A273400 A273401 A273402 * A273404 A273405 A273406`
	KEYWORD	`nonn,more,hard`
	AUTHOR	`Tim Johannes Ohrtmann, May 21 2016`
	EXTENSIONS	`a(7)-a(9) from Jon Grantham, Jul 29 2023`
	STATUS	`approved`