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 60th year, we have over 367,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A339867 Primes p such that p + sigma(p-1) and p + sigma(p+1) are both prime. 1
 13, 23, 41, 43, 53, 59, 61, 67, 131, 167, 193, 227, 263, 271, 283, 293, 311, 313, 397, 503, 523, 563, 571, 599, 607, 631, 653, 661, 701, 743, 827, 839, 907, 911, 919, 941, 947, 1031, 1087, 1103, 1171, 1181, 1187, 1301, 1319, 1321, 1381, 1499, 1531, 1559, 1619, 1621, 1663, 1741, 1747, 1811, 1847 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Terms with sigma(p-1) = sigma(p+1) include 919, 334541 and 463219. LINKS Robert Israel, Table of n, a(n) for n = 1..10000 EXAMPLE a(3) = 41 is a term because 41 is prime, 41 + sigma(40) = 41+1+2+4+5+8+10+20+40=131 is prime, and 41 + sigma(42) = 41+1+2+3+6+7+14+21+42=137 is prime. MAPLE select(t -> isprime(t + numtheory:-sigma(t-1)) and isprime(t + numtheory:-sigma(t+1)), [seq(ithprime(i), i=1..300)]) CROSSREFS Cf. A339862, A000203. Sequence in context: A164494 A164407 A259216 * A135283 A225519 A213655 Adjacent sequences: A339864 A339865 A339866 * A339868 A339869 A339870 KEYWORD nonn AUTHOR J. M. Bergot and Robert Israel, Dec 19 2020 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 7 23:30 EST 2023. Contains 367662 sequences. (Running on oeis4.)