

A189536


The smallest prime p such that tau(p1) + tau(p+1) = prime(n), or 0 if no such prime exists; where tau(k) is the number of divisors of k.


0



0, 2, 3, 5, 17, 37, 101, 0, 401, 3137, 4357, 62501, 21317, 16901, 1008017, 15877, 1020101, 33857, 69697, 14401, 331777, 78401, 32401, 57601, 828101
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OFFSET

1,2


COMMENTS

This is sequence A090482(n) for prime n.


LINKS

Table of n, a(n) for n=1..25.


MATHEMATICA

nn = 25; t = Table[1, {nn}]; t[[1]] = 0; t[[8]] = 0; cnt = 2; p = 1; While[cnt < nn, p = NextPrime[p]; s = DivisorSigma[0, p  1] + DivisorSigma[0, p + 1]; If[PrimeQ[s], i = PrimePi[s]; If[i <= nn && t[[i]] == 1, t[[i]] = p; cnt++]]]; t (* T. D. Noe, Apr 28 2011 *)


CROSSREFS

Cf. A000005, A000668, A002496, A090482, A175144 (tau(p1)+tau(p+1)).
Sequence in context: A077498 A118958 A259596 * A163588 A053182 A211972
Adjacent sequences: A189533 A189534 A189535 * A189537 A189538 A189539


KEYWORD

nonn


AUTHOR

JuriStepan Gerasimov, Apr 23 2011


STATUS

approved



