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%I #8 Dec 21 2020 02:05:13
%S 13,23,41,43,53,59,61,67,131,167,193,227,263,271,283,293,311,313,397,
%T 503,523,563,571,599,607,631,653,661,701,743,827,839,907,911,919,941,
%U 947,1031,1087,1103,1171,1181,1187,1301,1319,1321,1381,1499,1531,1559,1619,1621,1663,1741,1747,1811,1847
%N Primes p such that p + sigma(p-1) and p + sigma(p+1) are both prime.
%C Terms with sigma(p-1) = sigma(p+1) include 919, 334541 and 463219.
%H Robert Israel, <a href="/A339867/b339867.txt">Table of n, a(n) for n = 1..10000</a>
%e 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.
%p select(t -> isprime(t + numtheory:-sigma(t-1)) and isprime(t + numtheory:-sigma(t+1)), [seq(ithprime(i),i=1..300)])
%Y Cf. A339862, A000203.
%K nonn
%O 1,1
%A _J. M. Bergot_ and _Robert Israel_, Dec 19 2020
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