A228076 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A228076

Numbers k such that (19^k - 4^k)/15 is prime.

2, 7, 11, 31, 47, 139, 263, 769, 20551, 21491, 112247

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

All terms are prime.

a(12) > 2*10^5.

LINKS

Table of n, a(n) for n=1..11.

MATHEMATICA

Select[Prime[Range[1, 100000]], PrimeQ[(19^# - 4^#)/15]&]

PROG

(PARI) is(n)=ispseudoprime((19^n-4^n)/15) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

Cf. A224691, A128354, A128032.

Sequence in context: A327552 A336342 A284354 * A123151 A371201 A026133

Adjacent sequences: A228073 A228074 A228075 * A228077 A228078 A228079

KEYWORD

nonn,hard,more

AUTHOR

Robert Price, Aug 09 2013

EXTENSIONS

a(11) from Robert Price, Mar 06 2021

STATUS

approved