

A211660


Numbers k such that k and k+2 both have unique values of sigma(k) and sigma(k+2); sigma(k) = A000203(k) = sum of divisors of k.


8



1, 2, 3, 5, 7, 27, 43, 98, 146, 169, 171, 197, 200, 217, 241, 257, 281, 331, 347, 379, 386, 409, 448, 461, 487, 505, 507, 509, 547, 554, 576, 577, 641, 800, 821, 829, 841, 857, 907, 937, 1117, 1250, 1261, 1283, 1289, 1322, 1352, 1359, 1387, 1415, 1601, 1621
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OFFSET

1,2


COMMENTS

Subsequence of A211656. Number k is in sequence iff k and k+2 are in A211656.
Supersequence of A211767 (lesser of twin primes p, p+2 with unique values of sigma(p) and sigma(p+2)).


LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000


EXAMPLE

Number 27 is in sequence because sigma(27) = 40, sigma(29) = 30 and there are no other numbers m, n with sigma(m) = 40 or sigma(n) = 30.


CROSSREFS

Cf. A000203, A211656, A211657, A211658, A211659, A211767, A211768, A211769.
Sequence in context: A333955 A333960 A273726 * A215155 A228486 A117135
Adjacent sequences: A211657 A211658 A211659 * A211661 A211662 A211663


KEYWORD

nonn


AUTHOR

Jaroslav Krizek, Apr 20 2012


STATUS

approved



