

A067829


Primes n such that sigma(n2) < n.


5



3, 5, 7, 13, 19, 31, 43, 61, 73, 103, 109, 139, 151, 181, 193, 199, 229, 241, 271, 283, 313, 349, 421, 433, 463, 523, 571, 601, 619, 643, 661, 811, 823, 829, 859, 883, 1021, 1033, 1051, 1063, 1093, 1153, 1231, 1279, 1291, 1303, 1321, 1429, 1453, 1483, 1489
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OFFSET

1,1


COMMENTS

Also, apart from the first term, greater members of twin prime pairs: A006512(n) = a(n+1).  Reinhard Zumkeller, Dec 07 2002
Smallest prime > nth odd number that is the difference of 2 primes.  JuriStepan Gerasimov, Nov 08 2010
These primes are the only primes, p(j) = A000040(j), such that (p(j)p(jm)) divides (p(j)+p(jm)) for some m, 0 < m < j. For all such cases, m=1. It is easy to prove for jm>1 the only common factor of (p(j)p(jm)) and (p(j)+p(jm)) is 2, and there are no common factors if jm = 1. Thus, p(jm) is the lesser member of a twin prime pair, except when j=2.  Richard R. Forberg, Mar 25 2015


LINKS

Table of n, a(n) for n=1..51.


MATHEMATICA

Select[Prime@ Range@ 240, DivisorSigma[1, #  2] < # &] (* Michael De Vlieger, Jun 12 2015 *)


PROG

(PARI) lista(nn) = forprime(p=3, nn, if (sigma(p2) < p, print1(p, ", ")); ); \\ Michel Marcus, Jun 06 2015


CROSSREFS

Cf. A025584, A001359, A006512, A000203.
Sequence in context: A111703 A184248 A206023 * A084696 A330222 A154700
Adjacent sequences: A067826 A067827 A067828 * A067830 A067831 A067832


KEYWORD

nonn


AUTHOR

Benoit Cloitre, Feb 08 2002


STATUS

approved



